Liquid crystal display device and thin film transistor substrate

ABSTRACT

In a vertically aligned liquid crystal display device for controlling liquid crystal molecules alignment in voltage application by providing linear structures or linear slits consisting of a plurality of constituent units to at least one of a pair of substrates having an electrode thereon, there is provided alignment controlling means for forming an alignment singular point s=−1 of liquid crystal molecules at an intersecting point between the structures on the pixel electrode or the slits in the electrode and an edge of a pixel electrode on one of the substrates.

This is a divisional of application Ser. No. 09/662,236, filed Sep. 14,2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) deviceand a thin film transistor substrate and, more particularly, a VA(Vertically aligned) mode liquid crystal display device and a thin filmtransistor substrate.

2. Description of the Prior Art

The liquid crystal display device is employed in various electronicdevices, e.g., is employed as not only the display of the mobilecomputer, but also the display of the desk-top computer, the display ofthe television, the projector, the personal digital assistant (PDA),etc.

The normal TN (Twisted Nematic) mode liquid crystal display device hassuch a structure that the liquid crystal is sealed between twotransparent substrates. Out of two surfaces of these transparentsubstrates opposing to each other, the common electrode, the colorfilter, the alignment film, etc. are formed on one surface side, and thethin film transistor (TFT), the pixel electrodes, the alignment film,etc. are formed on the other surface side. Also, polarizing plates arestuck on the opposing surfaces and the opposite side surfaces of thetransparent substrates respectively. These two polarizing plates arearranged such that, for example, their polarization axes can intersectperpendicularly to each other. In this case, two polarizing plates givethe light display (white display) to transmit the light in the conditionthat the voltage is not applied between the pixel electrode and thecommon electrode, while they give the dark display (black display) tocut off the light in the condition that the voltage is applied. Incontrast, if the polarization axes of two polarizing plates are arrangedin parallel with each other, two polarizing plates give the dark displayin the condition that the voltage is not applied between the pixelelectrode and the common electrode, while they give the light display inthe condition that the voltage is applied. In the following description,the substrate on which TFT and the pixel electrodes are formed is calledthe TFT substrate, while the substrate on which the color filters andthe common electrode are formed is called the opposing substrate.

The TN mode liquid crystal display device has such drawbacks that theviewing angle is narrow and the resolution is not sufficient.

FIGS. 1A to 1C are views showing these drawbacks. FIG. 1A shows thestate to display the white by not applying the voltage between twoelectrodes 101, 102, FIG. 1B shows the state to display the half tone(gray) by applying the intermediate voltage V1 between two electrodes101, 102, and FIG. 1C shows the state to display the black by applyingthe predetermined voltage V2 between two electrodes 101, 102.

In FIGS. 1A to 1C, alignment films 103, 104 are formed on the opposingsurfaces of two electrodes 101, 102 to differentiate their alignmentdirections by 90° (degrees) respectively. Also, although not shown, thepolarizing plates are arranged on respective outsides of two electrodes101, 102 in the condition that their linearly polarized directions aretwisted mutually by 90 degrees. In this case, actually liquid crystalmolecules L shown in FIGS. 1A to 1C are twisted in compliance with thealignment direction of the alignment films 103, 104, but they areillustrated herein not to take account of the twist, for the convenienceof explanation.

Meanwhile, as shown in FIG. 1A, in the condition that the voltage is notapplied, the liquid crystal molecules L are aligned in the samedirection to have a very small tilt angle (about 1 degree to 5 degrees).In this state, the display looks like almost white from all directions.

Also, as shown in FIG. 1C, in the condition that the voltage V2 isapplied, the liquid crystal molecules L are aligned in the perpendiculardirection to the alignment films 103, 104 except the neighborhood oftheir surfaces. Since the incident linearly polarized light isintercepted by the plate, the display looks like the black from theoutside. At this time, since the light irradiated obliquely into oneelectrode 101 passes obliquely to the direction of the liquid crystalmolecules L aligned in the vertical direction to thus twist itspolarization direction to some extent, the display looks like not theperfect black but the half tone (gray) from the outside.

In addition, as shown in FIG. 1B, in the condition that the intermediatevoltage V1 lower than the state in FIG. 1C is applied, the liquidcrystal molecules L positioned in vicinity of the alignment films 103,104 are also aligned in the horizontal direction, but the liquid crystalmolecules L rise obliquely in the middle area of the cell. Therefore,the double refraction (birefringence) property of the liquid crystal islost in some degree to lower the transmittance and thus the half tone(gray) display appears. However, this is true of only the light L1 thatis irradiated vertically to the liquid crystal panel. The light that isirradiated obliquely to the surface of one electrode 101 exhibitsdifferent behaviors when the display is viewed from the left and rightdirections in FIG. 1B.

In other words, in FIG. 1B, the direction of the liquid crystalmolecules L becomes parallel with the light L2 that is directed from thelower right to the upper left. Therefore, since the liquid crystal Lseldom exhibits the double refraction effect, the display looks like theblack when it is viewed from the left side. On the contrary, thedirection of the liquid crystal molecules L becomes perpendicular to thelight L3 that is directed from the lower left to the upper right.Therefore, since the liquid crystal L exhibits greatly the doublerefraction effect to the incident light to twist the incident light, thedisplay looks like a color close to the white. That is, the displayintensity is changed according to the viewing angle, and this aspect isthe biggest drawback of the TN mode liquid crystal display device.

For this reason, as the mode that can improve the viewing anglecharacteristic without reduction of the response speed, the VA(Vertically Aligned) mode using the vertical alignment films has beenproposed.

FIGS. 2A to 2C are views showing the VA mode. The VA mode uses thenegative type liquid crystal material and the vertical alignment filmsin combination.

First, as shown in FIG. 2A, when the voltage is not applied, the liquidcrystal molecules L are aligned in the vertical direction to provide theblack display. In the VA mode, the vertically aligning process isapplied to the alignment films 103, 104.

Also, as shown in FIG. 2C, when the predetermined voltage V2 is appliedbetween two electrodes 101, 102, the liquid crystal molecules L arealigned in the horizontal direction to provide the while display. The VAmode has the high display contrast, the quick response speed, and thevisual characteristic in the white display and the black display ratherthan the TN mode.

In addition, as shown in FIG. 2B, when the predetermined voltage V1smaller than that in the white display is applied between two electrodes101, 102, the liquid crystal molecules L are aligned in the obliquedirection. In this case, the light that is perpendicular to the surfaceof the electrode 101 is displayed as the half tone on the display panel.However, in FIG. 2B, the liquid crystal molecules L are parallel withthe light L2 directed from the lower right to the upper left.Accordingly, since the liquid crystal molecules L seldom exhibits thedouble refraction effect, the display looks like the black if it isviewed from the left side. In contrast, the liquid crystal molecules Lare vertical to the light L3 directed from the lower left to the upperright. Accordingly, since the liquid crystal molecules L exhibitsgreatly the double refraction effect to the incident light to twist theincident light, the display that is close to the white is given.

In this manner, since the liquid crystal molecules positioned in theneighborhood of the alignment films become substantially vertical whenthe voltage is not applied, the VA mode has the especially high contrastand also is excellent in the viewing angle characteristic rather thanthe TN mode. However, the VA mode has the problem similar to the TNmode, i.e., when the half tone display is performed in the VA mode, thedisplay intensity is changed if the viewing angle is changed. Thus, theVA mode is still not enough in the aspect of the viewing anglecharacteristic.

In Patent Application Hei 10-185836, the applicant of this applicationdiscloses the configuration in which vertical alignment in the prior artis used, the liquid crystal material having the negative dielectricanisotropy, so-called negative type liquid crystal, is sealed betweenthe electrodes, and the domain defining means for defining the liquidcrystal molecules to differentiate their tilt directions in a pluralityof regions in one pixel when the voltage is not applied is provided.

FIGS. 3A to 3C are views showing the visual characteristic improvingprinciple by using alignment division. In this case, the structure isemployed in which the slit S is formed in one pixel electrode 111 on thefirst substrate side as the domain defining means and the projection Pis provided in one pixel on the electrode 112 on the second substrateside.

As shown in FIG. 3A, when the voltage is not applied, the liquid crystalmolecules are aligned perpendicularly to the substrate surface. Also, asshown in FIG. 3C, when the predetermined voltage V2 is applied betweenthe opposing electrodes 111, 112, the liquid crystal molecules arealigned in parallel with the substrate surface to provide the whitedisplay.

In addition, as shown in FIG. 3B, when the intermediate voltage V1 isapplied between the opposing electrodes 111, 112, the electric fieldthat is oblique to the substrate surface is generated due to the slit(electrode edge portion) S. Also, the liquid crystal molecules L in theneighborhood of the surface of the projection P are slightly tilted fromthe state when no voltage is applied. The tilt directions of the liquidcrystal molecules L are decided by the influence of inclined surfaces ofthe projection P and the oblique electric field. Thus, the alignmentdirections of the liquid crystal molecules 113 are divided in the middleof the projection P and in the middle of the slit portion 111 srespectively.

At this time, since the liquid crystal molecules L are slightly tilted,for example, the light L1 that is transmitted from the bottom of thesubstrate to the top is affected slightly by the double refraction tosuppress the transmission. Thus, the half tone display of gray can beobtained. The light L2 transmitted from the lower right to the upperleft is hard to transmit in the area in which the liquid crystalmolecules L are tilted to the left direction, but such light L2 is veryeasy to transmit in the area in which the liquid crystal molecules L aretilted to the right direction. Thus, the half tone display of gray canbe obtained as the average. In addition, the light L3 transmitted fromthe lower left to the upper right exhibits the gray display based on thesimilar principle. As a result, the uniform half tone display can beobtained in all directions in one pixel.

Therefore, in FIG. 3B, the good display that has the small viewing angledependency can be obtained in all the black, half tone, and whitedisplay states.

In FIGS. 3A to 3C, the slit S is formed in one pixel electrode 111 onthe first substrate side as the domain defining means, and theprojection P is provided in one pixel on the electrode 112 on the secondsubstrate side. But such structure may be accomplished by other means.Such new VA mode is referred to as the MVA (Multi-domain VerticalAlignment) mode in the following.

FIGS. 4A to 4C are views showing examples for implementing the domaindefining means.

FIG. 4A shows an example in which the domain defining means isimplemented only by using the electrode shapes, FIG. 4B shows an examplein which shapes of the substrate surfaces are designed, and FIG. 4Cshows an example in which shapes of the electrodes and the substratesurfaces are designed. Although the alignments shown in FIGS. 3A to 3Ccan be obtained in all these examples, respective structures areslightly different.

Next, the case where projections are provided on the opposing surfacesof two substrates, as shown in FIG. 4B, will be explained as an examplehereunder.

In FIG. 4B, projections P1, P2 for dividing the alignment directionsalternatively are formed on the electrodes 111, 112 on the opposingsurfaces of two substrates, and also vertical alignment films 113, 114are provided on the inner surfaces of them. The vertical aligningprocess is applied to the vertical alignment films. The liquid crystalinjected between two substrates is the negative type one. When novoltage is applied, the liquid crystal molecules L are alignedperpendicularly to the substrate surface on the vertical alignmentfilms. Since the liquid crystal molecules L tend to be alignedperpendicularly to the inclined surfaces of the projections P1, P2, suchliquid crystal molecules L on the projections P1, P2 are also tilted.However, since the liquid crystal molecules L are aligned almostperpendicularly to the substrate surface in most areas except for theprojections P1, P2 when no voltage is applied, the good black displaycan be obtained, as shown in FIG. 3A.

When the voltage is applied, the liquid crystal molecules L are parallelwith the substrate (the electric field is perpendicular to thesubstrate) in areas in which the projections P1, P2 are not provided,but such liquid crystal molecules L are tilted in vicinity of theprojections P1, P2. In other words, when the voltage is applied, theliquid crystal molecules L are tilted in response to the intensity ofthe electric field but the electric field is directed perpendicularly tothe substrate. Therefore, unless the tilt direction of the liquidcrystal molecules L is defined by the rubbing, the liquid crystalmolecules L may take all directions of 360 degrees as the tilted azimuthto the electric field. Since the electric field is inclined in thedirection parallel with the inclined surfaces of the projections P1, P2on the projections P1, P2, the liquid crystal molecules L are tilted inthe direction perpendicular to the electric field when the voltage isapplied. This direction coincides with the original direction inclinedby the projections P1, P2, and thus the liquid crystal molecules L arealigned more stably. In this manner, the projections P1, P2 can providethe stable alignment by both effects of their inclination and theelectric field on the inclined surface. In addition, if the largevoltage is applied, the liquid crystal molecules L are aligned in almostparallel with the substrate.

As described above, the projections P1, P2 can perform a role of thetrigger that decides the alignment azimuth of the liquid crystalmolecules L when the voltage is applied.

In FIG. 4A, slits S1, S2 are provided on both or either of electrodes111, 112. The vertical aligning process is applied to the alignmentfilms 113, 114, and the negative type liquid crystal is sealed betweenthe substrates. The liquid crystal molecules L are alignedperpendicularly to the substrate surface when no voltage is applied,whereas the electric field is generated at the slits (electrode edgeportions) S1, S2 in the oblique direction to the substrate surface whenthe voltage is applied. The tilt directions of the liquid crystalmolecules L are decided by the influence of this oblique electric field,and thus the alignment directions of the liquid crystal molecules aredivided in the right and left directions, as shown in FIG. 4A.

FIG. 4C shows an example in which the modes in FIG. 4A and FIG. 4B arecombined together. The slits S are formed in one electrode 111 while theprojections are provided on the other electrode 112. Though examples forimplementing three domain defining means are illustrated as above,various variations may be adopted.

FIG. 5 is a plan view showing positional relationships among bus lines,projections, pixels, and electrodes in the liquid crystal display panelin which the alignment of the liquid crystal molecules are divided intofour directions. FIG. 6 is a sectional view taking along a I—I line inFIG. 5.

In FIG. 5 and FIG. 6, a plurality of gate bus lines 122 extending in theX direction (the lateral direction in FIG. 5 and FIG. 6) are formed onthe TFT substrate 121 at a distance along the Y direction (thelongitudinal direction in FIG. 5 and FIG. 6). Also, capacitive bus lines123 extending in the X direction are formed between the gate bus lines122. Auxiliary capacitive branch lines 123 a that have a length not totouch the gate bus lines 122 are formed from the capacitive bus lines123 in the Y direction so as to oppose to a part of drain bus lines(also called data bus lines), described later.

The gate bus lines 122 and the capacitive bus lines 123 are covered witha first insulating film 124. Then, a plurality of drain bus lines 125extending in the Y direction are formed in the X direction on the firstinsulating film 124 at a distance. The TFTs 126 are formed to correspondto crossing portions between the gate bus lines 122 and the drain buslines 125. The TFT 126 has a semiconductor layer 126 a formed on thegate bus line 122 via the first insulating film 124, a drain electrode126 d formed on the semiconductor layer 126 a, and a source electrode126 s formed on the semiconductor layer 126 a. The drain electrode 126 dis connected to the neighboring drain bus lines 125. The drain bus lines125 and the TFTs 126 are covered with a second insulating film 127.

A pixel electrode 128 made of ITO (indium-tin oxide) is formed on thesecond insulating film 127 and in the area surrounded by two drain buslines 125 and two gate bus lines 122. The pixel electrode 128 isconnected to the source electrode 126 s via a hole in the secondinsulating film 127.

The capacitive bus line 123 is hold at a constant potential. If thepotential of the drain bus line 125 is varied, the potential of thepixel electrode 128 is also varied based on the capacitive coupling dueto the stray capacitance. According to the configuration in FIG. 6,since the pixel electrode 128 is connected to the capacitive bus line123 via auxiliary capacitances, variation in potential of the pixelelectrode 128 can be reduced.

In FIG. 6, a color filter 132, a black matrix 133, a common electrode134, and an alignment film 135 are formed in sequence on an opposingsubstrate 131 opposing to the TFT substrate 121.

Also, projections 130, 136 that have zig-zag bending patterns to extendin the Y direction are formed on the opposing surfaces of the opposingsubstrate 131 and the TFT substrate 121 respectively. A bending angle ofthe bending pattern is roughly 90 degrees.

The projections 130 formed on the TFT substrate 121 side are aligned atan equal interval in the X direction, and their bending points arepositioned in the almost center of the gate bus lines 122. Theprojections 136 formed on the opposing substrate 131 have a patternsubstantially similar to the projections 130 formed on the TFT substrate121, and are formed on the common electrodes 134 such that they arepositioned in the almost middle portion between a plurality ofprojections 130 on the TFT substrate 121.

The projections 130 on the TFT substrate 121 side and the pixelelectrodes 128 are covered with the alignment film 129, while theprojections 136 on the opposing substrate 131 side are also covered withanother alignment film 135. Both the projections 130 on the TFTsubstrate 121 side and the projections 136 on the opposing substrate 131side intersect with edges of the pixel electrodes 128 at an angle of 45degrees respectively.

Also, polarizing plates (not shown) are arranged on the surfaces of theTFT substrate 121 and the opposing substrate 131, which do not put theliquid crystal material between them, respectively. These polarizingplates are arranged such that their polarization axes intersect withlinear portions of the projections 130, 136 by 45 degrees to formcross-nicol. That is, the polarization axis of one polarizing plate isparallel with the X direction in FIG. 6 and the polarization axis of theother polarizing plate is parallel with the Y direction in FIG. 6.

The TFT substrate 121 and the opposing substrate 131 are arranged inparallel at a distance mutually, and the liquid crystal material 139 isfilled into a space between them. The liquid crystal material 139 havingthe negative dielectric anisotropy is employed, as described above. Theprojections 130, 136 are formed of material that has the dielectricconstant equivalent to or less than that of the liquid crystal material139.

Next, the alignment of the liquid crystal molecules L when theintermediate voltage is applied to the pixel electrodes will beexplained, by taking as an example the case where the slits are formedin the pixel electrode, hereunder.

FIG. 7 is a plan view showing positional relationship among the gate buslines, the drain bus lines, the capacitive bus lines, and the pixelelectrode 128 formed on the TFT substrate on which the slits S areprovided on the pixel electrode in place of the projections 130 shown inFIG.5.

In FIG. 7, the pixel electrode 128 a is divided into a plurality ofareas by a plurality of slits S passing between upper projections 136 a.These areas are conductively connected mutually by connecting portions128 b that are formed to cross the slits S. Two slits S formed in theneighborhood of the center of the pixel electrode 128 a are intersectedwith each other at the edge portion of the pixel electrode 128 a.

Then, when the intermediate voltage is applied to the pixel electrode128 a, the liquid crystal molecules L on the pixel electrode 128 a aretilted to the surface of the pixel electrode 128 a. The liquid crystalmolecule L in FIG. 7 is indicated by a circular cone. A vertex of thecircular cone indicates a position of one end of the liquid crystalmolecule on the TFT substrate side, and a base of the circular coneindicates a position of the other end of the liquid crystal molecule.Four types of the tilt direction of the liquid crystal molecule L aregiven based on the principle shown in FIG. 4.

As described above, the MVA mode is the mode in which the liquidcrystals having the negative dielectric anisotropy are alignedsubstantially perpendicularly to the substrate surface. Since the MVAmode can have the high contrast and can improve the visualcharacteristic without reduction of the switching speed, its displayquality is good. In addition, the viewing angle characteristic can beimproved much more by using the domain defining means.

FIG. 8 is a sectional view showing another MVA liquid crystal displaydevice in the prior art. First projections 167 are formed on theopposing surface of a glass substrate 151, and second projections 168are formed on the opposing surface of a glass substrate 186. The firstprojections 167 and the second projections 168 extend in the directionperpendicular to the sheet of FIG. 8, and are arranged alternately alongthe lateral direction in FIG. 8. A vertical alignment film 178 is formedon the opposing surfaces of the glass substrates 151, 186 respectivelyto cover the projections 167, 168.

Liquid crystal material 179 containing liquid crystal molecules 180 isfilled between the glass substrate 151 and the glass substrate 186. Theliquid crystal molecules 180 have the negative dielectric anisotropy.The dielectric constant of the projections 167, 168 is lower than thatof the liquid crystal material 179. Polarizing plates 181, 182 arecross-nicol-arranged on the outside of the glass substrate 151 and theglass substrate 186 respectively. Since the liquid crystal molecules 180are aligned vertically to the substrate surface when the voltage is notapplied, the good dark state can be obtained.

When the voltage is applied between the substrates, equipotentialsurfaces indicated by a broken line 166 appear. Since the dielectricconstant of the projections 167, 168 is smaller than that of the liquidcrystal layers, the equipotential surfaces 166 in the neighborhood ofthe side surfaces of the projections 167, 168 are inclined to come downin the projections. Therefore, the liquid crystal molecules 180 a in theneighborhood of the side surfaces of the projections 167, 168 are tiltedto become parallel to the equipotential surfaces 166. The peripheralliquid crystal molecules 180 a are tilted by the influence of thetilting of the liquid crystal molecules 180 a. For this reason, theliquid crystal molecules 180 between the first projections 167 and thesecond projections 168 are aligned such that their major axis (director)is inclined right- upward in FIG. 8. The liquid crystal molecules 180positioned on the left side rather than the first projections 167 andthe liquid crystal molecules 180 positioned on the right side ratherthan the second projections 168 are aligned such that their major axis(director) is inclined right-downward in FIG. 8.

In this manner, a plurality of domains in which the tilt directions ofthe liquid crystal molecules are different are defined in one pixel. Thefirst projections 167 and the second projections 168 define boundariesof the domains. Two type domains can be formed by arranging the firstprojections 167 and the second projections 168 in parallel with thesubstrate surface mutually. Four type domains can be formed in total bybending patterns of these projections by 90 degrees. Since pluraldomains are formed in one pixel, the visual characteristic in the halftone display state can be improved.

The inventors of the present invention point out that the above liquidcrystal display device in the prior art has problems described in thefollowing.

The MVA mode liquid crystal display device can achieve the high picturequality, the high reliability, and the high productivity. However, theVA mode has essentially such a nature that it easily accepts theinfluence of the electric field because of its weak anchoring force incontrast to the horizontally aligned mode such as the TN mode, and thusthe MVA mode partakes of such nature of the VA mode.

Accordingly, as shown in FIGS. 9A and 9B, the alignment state of theliquid crystal molecules L around the pixel electrode 128 is changedbecause of changes of the gate bus line potential Egc and the drain busline potential (data voltage) Egs in some case. Such phenomenon occurssimilarly in the case of the TN mode, nevertheless the phenomenon isready to occur in the VA mode rather than the TN mode.

Also, as the phenomenon peculiar to the MVA mode, sometimes theprojections are charged under various conditions such as the drivingstate. At this time, the alignment of the liquid crystals at theintersecting portions between the drain bus lines and the gate bus linesis changed by the influence of the charge of the projections.

When the alignment around the pixel is changed, values of the straycapacitances, e.g., a gate-common electrode capacitance Cgc, agate-source capacitance Cgs, a drain- common electrode capacitance Cdc,etc. are also changed correspondingly. As a result, the potential of thepixel electrode 126 s is also changed by the capacitive coupling.Normally the potential variation of the pixel electrode is reduced bythe auxiliary capacitance, but such variation cannot be perfectlycompensated in some cases. The potential variation of the pixelelectrode is easily caused if the auxiliary capacitance is reduced toincrease the aperture ratio especially. If the potential of the pixelelectrode is varied, the flicker appears on the screen.

It may be considered that the auxiliary capacitance is increased to suchextent that the potential variation of the pixel electrode can beeliminated completely. If so, the aperture ratio is reducedcorrespondingly.

Next, generation of residual images in the MVA liquid crystal displaydevice will be explained hereunder.

The generation of residual images in the liquid crystal display deviceis caused by the abnormality of the response speed. This is because thedomain control direction on the above projections on the electrode andon the above slits is not defined.

Such unstability of the domain control direction is generated due tovariation in cell thickness, etc. Hence, the liquid crystal displaydevice in which the residual images are caused is not forwarded as thedefective product.

As the result of the examination to check the cause for the long-timeremaining residual images, followings become apparent.

In other words, as shown in FIGS. 10A and 10B, in the liquid crystaldisplay device employing the configuration in which a plurality ofprojections or slits are formed on the electrodes, it can be understoodthat, if there is a difference between the domain state when the displayis changed from the black to the white and the domain state when thedisplay is changed from the half tone to the white, the long-timeremaining residual images are generated.

In FIG. 10A, the number of domains on the slits S after the display ischanged from the black to the white are six because the domain isdivided by boundaries at middle positions (center positions of the slitsS) between all the connecting portions 128 b of the pixel electrode 128a. Therefore, the liquid crystal molecules L in the neighborhood of theslits S are aligned in the perpendicular direction to the straightportions of the slits S.

In contrast, in FIG. 10B, the number of domains on the slits S after thedisplay is changed in the order of the black, the half tone, and thewhite are two or four because the domain is divided by boundariesbetween a part of the connecting portions 128 b. Therefore, there existsan area in which the domains are not changed by boundaries between theconnecting portions 128 b and their middle portions. The liquid crystalmolecules L in vicinity of the slits S are aligned obliquely to thestraight portions of the slits S in this area.

One of the causes may be considered as follows. That is, since thevoltage is not sufficiently applied to the liquid crystal molecules L onthe projections 130 or the slits S in the half tone display, the liquidcrystal molecules L are aligned almost perpendicularly to the substratesurface, as shown in FIG. 11. Thus, influences of the electric field atthe edge of the pixel electrode 128 a and the alignment of the displaydomains being affected by such electric field affect the dividedportions of the alignment controlling means as the connecting portions.As a result, the alignment control effect achieved by dividing thealignment controlling means cannot be sufficiently performed. In otherwords, when the liquid crystal molecules L on the slits S or theprojections 130 are aligned perpendicularly in the half tone display,such neighboring liquid crystal molecules L are affected by the electricfield at the edges of the pixel electrode 128 a and then tilted to thestraight portions of the slits S or the projections 130.

Accordingly, when the display is changed from the half tone display tothe white display, the domain {circle around (3)} shown in FIG. 10Adisappears to connect the domains {circle around (2)} and {circle around(4)}, and then the domain {circle around (5)} disappears to connect thedomains {circle around (4)} and {circle around (6)}. As a result, asshown in FIG. 10B, the right-upward directed domains are connected andthe left-downward directed domains are disappeared, so that the domainson the slits S after the white display are reduced into two domains{circle around (1)} and {circle around (2)}.

As another one of the causes for generating the residual images, it maybe considered that the bending portions of the patterns of theprojections 130 or the slits S of the alignment controlling means arearranged at the edges of the pixel electrode 128 a. The alignment statesof the liquid crystal molecules L at the bending portions are any ofthree types shown in FIGS. 12A to 12C.

However, the alignment at the bending portions becomes as shown in FIG.12C since it is affected by the influence of the alignment by the edgesof the pixel electrode 128 a. As a result, as indicated by a dot-dashline in FIG. 13, the alignment control direction by the edges of thepixel electrode 128 a is extended into the pixel. Since this extensionaffects the alignment of the domains on the slits S in the case of thehalf tone display, the alignment control effect given by dividing thealignment controlling means cannot sufficiently be brought about.

Also, as shown in FIG. 14A and FIG. 14B, in the TFT substrate, sometimesthe area in which a plurality of electrodes are stacked, especially thepixel electrode 128 a and the capacitance electrode (capacitive busline) 123 are punched through the insulating film between them togenerate the short-circuit. At this time, in the liquid crystal displaydevice having the structure in which the pixel electrode 128 a isdivided into a plurality of areas by using the slits S as the alignmentcontrolling means and then these areas are electrically connected by theconnecting portions 128 b, as indicated by an X mark in FIGS. 14A and14B, the short-circuited area is disconnected from other areas bycutting off the connecting portions 128 b near the TFT 126 in the areaof the pixel electrode 128 a, that is short-circuited to the capacitivebus line 123, so that the liquid crystal molecules in the pixel can bepartially driven.

However, since the area that is short-circuited to the capacitive busline 123 of the pixel electrode 128 a is positioned in the center of thepixel, merely the half area or less of the pixel electrode 128 a can bedriven, as indicated by a dot-dash line in FIG. 14A, whereby this pixelarea acts as the point defect failure to lower yield of the device.

When the voltage is not applied, the liquid crystal molecules invicinity of the edges of the projections 167, 168 in the MVA liquidcrystal display device in the prior art shown in FIG. 8 are alignedalmost perpendicularly in the area in which the projections 167, 168 arenot formed. However, the liquid crystal molecules in the neighborhood ofthe edges of the projections 167, 168 are affected by the inclinedsurfaces of the projections and thus tilted to the substrate surface.Therefore, the double refraction effect appears against the light beingtransmitted in the thickness direction of the liquid crystal layer.Because of this double refraction effect, the light is transmittedslightly when the display is to be in the dark state, and thus loweringof the contrast is brought out.

The leakage of light in the dark state can be prevented by covering theareas located in the neighborhood of the inclined surfaces of theprojections with a light-shielding film. Nevertheless, if suchlight-shielding film is provided, the light is shielded even in thelight state and thus reduction of the transmittance (the aperture ratio)is brought about.

Also, in the MVA liquid crystal display device shown in FIG. 8 in theprior art, the liquid crystal molecules 180 are tilted when the voltageis applied, but the tilt directions of the liquid crystal molecules inthe area located far from the projections 167, 168 are not directlydecided. That is, the liquid crystal molecules 180 a in the neighborhoodof the projections 167, 168 are tilted and the tilt is propagatedsequentially up to the area far from the projections 167, 168. In thismanner, the tilt directions of the liquid crystal molecules 180 in thearea far from the projections 167, 168 are indirectly decided. Sincedistortion of the electric field is small at the time of the half tonedisplay state, the propagation speed of the tilt of the liquid crystalmolecules is lowered. Therefore, the response from the dark state to thehalf tone state is delayed.

Also, the transmission loss of the light is ready to generate in theneighborhood of the projections provided in the MVA liquid crystaldisplay device. Therefore, there is such a tendency that thetransmittance (aperture ratio) is reduced in contrast to the TN modeliquid crystal display device. In case the liquid crystal display deviceis used as the floor type one, the reduction in the transmittance doesnot become a large issue. Nevertheless, in order to install the liquidcrystal display device onto the mobile device, it is desired to enhancethe transmittance.

Upon the progress of the lower consumption power of the liquid crystaldisplay device, it is one of important subjects to increase the apertureratio. In the MVA mode liquid crystal display device, the alignmentdivision (multi-domain) can be accomplished by forming the domaindefining projections (so-called banks) on the TFT substrate and theopposing substrate respectively, and thus the good viewing anglecharacteristic and the good picture quality can be derived. In thiscase, the aperture ratio is reduced because of the projections in thepixel area.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid crystaldisplay device capable of achieving a good picture quality.

The above subjects can be overcome by providing, as shown in FIG. 25, avertically aligned liquid crystal display device for controlling liquidcrystal molecules alignment in voltage application by providing linearstructures or linear slits consisting of a plurality of constituentunits to at least one of a pair of substrates having an electrodethereon, comprising: alignment controlling means for forming analignment singular point s=−1 of liquid crystal molecules at anintersecting point between the structures on the electrode or the slitsin the electrode and an edge of a pixel electrode on one of thesubstrates.

According to the present invention, in the liquid crystal display devicehaving at least one of the structures on the electrode, that is used asthe domain defining means, or the slits in the electrode, the alignmentsingular point s=−1 or s=+1 of the liquid crystal molecules is formed inthe neighborhood of the intersecting portion between the prolonged lineof the structures or the slits and the edge of the pixel electrode.

As for the change of the domains of the liquid crystal molecules on theslits if the present invention is applied, as shown in FIG. 32A, forexample, when the display is changed from the black display to the whitedisplay, the number of domains divided by the connecting portions on theslit is eight such as {circle around (1)} to {circle around (8)}. Also,according to FIG. 32A, the domains {circle around (8)} and {circlearound (9)} are increased in number rather than FIG. 10A indicating theproblem in the prior art. This is because the singular point s=−1 of thealignment vector is formed at the edge of the pixel electrode. Then, asshown in FIG. 32B, when the display is changed from the black display tothe white display via the half tone display, the domains {circle around(6)} and {circle around (8)} are connected and thus the domain {circlearound (7)} disappears. In other words, the change of domains on theslits can be suppressed at a very small level rather than FIG. 10A inthe neighborhood of the edge of the pixel electrode.

Accordingly, difference of the domain states between the white monitoredwhen the display of the pixel is changed from the black display to thewhite display and the white monitored when the display of the pixel ischanged from the half tone display to the white display can be reducedto an unobtrusive level, so that the domain change can be reduced up toa undistinguishable level as the residual image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views showing changes in images according to aviewing angle of the TN mode liquid crystal display device in the priorart;

FIGS. 2A to 2C are views showing driving states of the VA liquid crystaldisplay device in the prior art;

FIGS. 3A to 3C are views showing an effect of alignment division in theVA mode in the prior art;

FIGS. 4A to 4C are views showing various modes of alignment division inthe prior art;

FIG. 5 is a plan view showing a pixel portion in the MVA mode in theprior art;

FIG. 6 is a sectional view showing the pixel portion in the MVA mode inthe prior art, taking along a I—I line in FIG. 5;

FIG. 7 is a plan view showing a pixel portion in the MVA mode in theprior art;

FIG. 8 is a sectional view showing an MVA liquid crystal display devicein the prior art;

FIGS. 9A and 9B are views showing an OFF state and an ON state of an MVAliquid crystal panel in the prior art;

FIGS. 10A and 10B are views showing changes in the alignment directionof liquid crystal molecules in the MVA liquid crystal panel in the priorart;

FIG. 11 is a view showing the alignment direction of the liquid crystalmolecules in half tone display of the MVA mode in the prior art;

FIGS. 12A to 12C are views showing combinations of the alignmentdirection of the liquid crystal molecules on a slit on a pixel electrodein the MVA mode in the prior art;

FIG. 13 is a view showing the alignment direction of the liquid crystalmolecules in vicinity of an edge of the pixel electrode after the liquidcrystal display in the VA mode in the prior art is changed from the halftone display to the white display;

FIG. 14A is a plan view showing a cut-off state of the pixel electrodein the VA mode in the prior art, and FIG. 14B is an equivalent circuitdiagram in this state;

FIG. 15 is a plan view showing arrangement of domain defining means in apixel area according to a first embodiment of the present invention;

FIG. 16 is a plan view showing the pixel area in which a dielectricstructure and projections are formed, according to the first embodimentof the present invention;

FIG. 17 is a sectional view showing the pixel area according to thefirst embodiment of the present invention, taken along a II—II line inFIG. 16;

FIG. 18 is a sectional view showing the pixel area according to thefirst embodiment of the present invention, taken along a III—III line inFIG. 16;

FIG. 19 is a sectional view showing the pixel area according to thefirst embodiment of the present invention, taken along a IV—IV line inFIG. 16;

FIGS. 20A and 20B are sectional views showing an operation in the pixelarea according to the first embodiment of the present invention;

FIG. 21 is a plan view showing a pixel area of a liquid crystal displaydevice according to a second embodiment of the present invention;

FIG. 22 is a sectional view showing the pixel area of the liquid crystaldisplay device according to the second embodiment of the presentinvention, taken along a V—V line in FIG. 21;

FIG. 23 is a sectional view showing a TFT and its neighboring areaaccording to the second embodiment of the present invention, taken alonga VI—VI line in FIG. 21;

FIG. 24 is a sectional view showing a pixel area of a liquid crystaldisplay device according to a third embodiment of the present invention;

FIG. 25 is a plan view showing the pixel area of the liquid crystaldisplay device according to the third embodiment of the presentinvention;

FIGS. 26A and 26B are views showing the alignment direction of theliquid crystal molecules at an alignment singular point according to thethird embodiment of the present invention;

FIG. 27 is a plan view showing a pixel area of a liquid crystal displaydevice according to a fourth embodiment of the present invention;

FIG. 28 is a sectional view showing the pixel area of the liquid crystaldisplay device according to the fourth embodiment of the presentinvention, taken along a VII—VII line in FIG. 27;

FIG. 29 is a plan view showing a pixel area of a liquid crystal displaydevice according to a fifth embodiment of the present invention;

FIG. 30 is a plan view showing another pixel area of the liquid crystaldisplay device according to the fifth embodiment of the presentinvention;

FIG. 31A is a plan view showing a pixel area of a liquid crystal displaydevice according to a sixth embodiment of the present invention, andFIG. 31B is a view showing connection between areas in the pixelelectrode in the pixel area;

FIGS. 32A and 32B are views showing an example of an effect achieved bythe sixth embodiment of the present invention;

FIG. 33 is a plan view showing an MVA liquid crystal display deviceaccording to a seventh embodiment of the present invention;

FIG. 34 is a sectional view showing a TFT portion of the MVA liquidcrystal display device according to the seventh embodiment of thepresent invention;

FIG. 35 is a sectional view showing a pixel electrode portion of the MVAliquid crystal display device according to the seventh embodiment of thepresent invention;

FIG. 36 is a sectional view showing a substrate and a mask to explain amethod of manufacturing the MVA liquid crystal display device accordingto the seventh embodiment of the present invention;

FIG. 37 is a sectional view showing a projection of an MVA liquidcrystal display device according to an eighth embodiment of the presentinvention;

FIG. 38 is a sectional view showing a substrate and a mask to explain amethod of manufacturing the MVA liquid crystal display device accordingto the eighth embodiment of the present invention;

FIG. 39A is a sectional view showing a liquid crystal display deviceaccording to a ninth embodiment of the present invention, and FIG. 39Bis a plan view showing a liquid crystal layer to show tilt directions ofliquid crystal molecules;

FIG. 40 is a sectional view showing a liquid crystal display deviceaccording to a tenth embodiment of the present invention;

FIG. 41A is a sectional view showing a liquid crystal display deviceaccording to an eleventh embodiment of the present invention, and FIG.41B is a plan view showing liquid crystal layers to show tilt directionsof liquid crystal molecules;

FIG. 42 is a sectional view showing a liquid crystal display deviceaccording to a twelfth embodiment of the present invention;

FIG. 43 is a plan view showing the liquid crystal display deviceaccording to the twelfth embodiment of the present invention;

FIG. 44 is a plan view showing a liquid crystal display device accordingto a thirteenth embodiment of the present invention;

FIGS. 45A and 45B are plan views showing alignment states of the liquidcrystal molecules in a liquid crystal display device according to afourteenth embodiment of the present invention;

FIG. 46 is a plan view showing the alignment state of the liquid crystalmolecules in a liquid crystal display device according to a fifteenthembodiment of the present invention;

FIG. 47 is a plan view showing one pixel of an MVA liquid crystaldisplay device according to a sixteenth embodiment of the presentinvention;

FIG. 48 is a sectional view showing a sectional shape at a position of aXI—XI line in FIG. 47;

FIG. 49 is a view #1 showing an effect in the sixteenth embodiment ofthe present invention, wherein an alignment state of the liquid crystalmolecules is shown when auxiliary projections are arranged atpredetermined positions;

FIG. 50 is a view #2 showing an effect in the sixteenth embodiment ofthe present invention, wherein a state in which alignment failure of theliquid crystal molecules is generated is shown when the auxiliaryprojections are arranged at positions deviated from the predeterminedpositions;

FIG. 51 is a view #3 showing an effect in the sixteenth embodiment ofthe present invention, wherein a state in which no alignment failure ofthe liquid crystal molecules is generated because of a pre-tilt anglerevealing process is shown even when the auxiliary projections arearranged at the positions deviated from the predetermined positions;

FIG. 52 is a plan view showing a liquid crystal display device accordingto a seventeenth embodiment of the present invention;

FIG. 53 is a plan view showing a liquid crystal display device accordingto an eighteenth embodiment of the present invention;

FIG. 54 is a schematic sectional view showing the liquid crystal displaydevice according to the eighteenth embodiment of the present invention;

FIG. 55 is a view showing equipotential lines when a voltage is appliedbetween a pixel electrode and a common electrode, in the eighteenthembodiment of the present invention;

FIG. 56 is a graph showing a result to check whether or not disclinationis generated after a dielectric film is formed by using two typedielectric materials;

FIG. 57 is a view showing a problem caused when high dielectric portionsare arranged in the center between slit rows and low dielectric portionsare arranged at portions opposing to the slits;

FIGS. 58A and 58B are views showing a variation #1 of the eighteenthembodiment of the present invention; and

FIG. 59 is a view showing a variation #2 of the eighteenth embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained in detail withreference to the accompanying drawings hereinafter.

First Embodiment

FIG. 15 shows a planar state of a TFT substrate of one pixel of an MVAmode liquid crystal display device according to a first embodiment ofthe present invention, except for an insulating film and dielectricprojections. FIG. 16 is a plan view showing the state in which adielectric structure is formed on the TFT substrate shown in FIG. 15.FIG. 17 is a sectional view taken along a II—II line in FIG. 16. FIG. 18is a sectional view taken along a III—III line in FIG. 16. FIG. 19 is asectional view taken along a IV—IV line in FIG. 16.

In FIG. 15, a plurality of gate bus lines 2 that extend in the Xdirection (lateral direction in FIG. 15) are formed at a distance in theY direction (longitudinal direction in FIG. 15) on a first glasssubstrate (TFT substrate) 1 on which TFTs are formed.

A capacitive bus line (storage capacitance forming electrode) 3extending in the X direction is formed between the gate bus lines 2.Auxiliary capacitive branch lines 3 a that have a length not to touchthe gate bus lines 2 are formed from the capacitive bus line 3 in the Ydirection so as to oppose to a part of drain bus lines, described later.

The gate bus lines 2, the capacitive bus lines 3, and the auxiliarycapacitive branch lines 3 a are formed simultaneously.

In other words, the gate bus lines 2, the capacitive bus lines 3, andthe auxiliary capacitive branch lines 3 a are formed by forming analuminum film of 100 nm thickness and a titanium film of 50 nm thicknesson the first glass substrate 1 by the sputtering and then patterningthese films by the photolithography method. The reactive ion etching(RIE) method using a mixed gas of BCl₃ and Cl₂ is employed in thepatterning.

As shown in FIG. 17, the gate bus line 2 and the capacitive bus line 3is covered with a gate insulating film 4 formed of silicon nitride thatis formed by the plasma-enhanced chemical vapor deposition (PE-CVD)method to have a thickness of 400 nm. A plurality of drain bus lines 5extending in the Y direction are formed on the gate insulating film 4 inthe X direction at a distance.

A TFT (thin film transistor) 6 is formed as the active element in theneighborhood of an intersection point between the gate bus line 2 andthe drain bus line 5.

As shown in FIG. 18, the TFT 6 has an active layer 6 a formed via thegate insulating film 4 in a region to cross a part of the gate bus line2, a drain electrode 6 d formed on the active layer 6 a on one side ofthe gate bus line 2, and a source electrode 6 s formed on the activelayer 6 a on the other side of the gate bus line 2. The drain electrode6 d is connected to the adjacent drain bus line 5.

The drain electrode 6 d and the source electrode 6 s are separated on achannel protection film 6 b formed on a channel region of the activelayer 6 a.

The channel protection film 6 b is formed by the following method.

In other words, a silicon nitride film of 140 nm thickness is formed onthe active layer 6 a and the gate insulating film 4 by the PE-CVDmethod, and then photoresist (photosensitive resin) is coated on thesilicon nitride film. Then, a resist pattern is formed by exposing anddeveloping the photoresist. The exposure process has a first exposurestep of irradiating the exposure light onto the photoresist from thelower surface of the glass substrate 1 by using the gate bus line 2 asan exposure mask and a second exposure step of irradiating the exposurelight onto the photoresist from the upper surface of the glass substrate1 by using the normal exposure mask. Accordingly, edges of the resistpattern are defined by edges of the gate bus line 2. Then, the channelprotection film 6 b made of the silicon nitride film is formed byetching the silicon nitride film in the region, that is not covered withsuch resist pattern, by the wet method using the buffer hydrofluoricacid or the RIE method the hydrofluoric acid group gas.

In this case, the active layer 6 a is formed by patterning a undopedamorphous silicon film that is formed on the gate insulating film 4 bythe PE-CVD method to have a thickness of 30 nm.

Also, all the source electrode 6 s, the drain electrode 6 d, and thedrain bus line 5 are formed by forming an n⁺-type amorphous silicon filmof 30 nm thickness, a titanium film of 20 nm thickness, an aluminum filmof 75 nm thickness, and a titanium film of 80 nm thickness in sequenceon the gate insulating film 4 and the channel protection film 6 b andthen patterning these films by using as a sheet of mask. This etching iscarried out by the RIE method using a mixed gas of BCl₃ and Cl₂. Thechannel protection film 6 b acts as an etching stopper in this etching.

The TFT 6 and the drain bus line 5 are covered with a protectioninsulating film 7 formed of silicon oxide or silicon nitride.

Also, a transparent pixel electrode 8 made of ITO having a thickness of70 nm is formed on the protection insulating film 7 in a regionsurrounded by two drain bus lines 5 and two gate bus lines 2. Thepatterning of the ITO film is carried out by the wet etching methodusing oxalic acid group etchant.

The pixel electrode 8 is electrically connected to the source electrode6 s through a hole 7 a in the protection insulating film 7.

Insulating projections 10 having zig-zag bending patterns extending inthe Y direction are formed on the protection insulating film 7 and thepixel electrode 8 at a distance in positions indicated by a chaindouble-dashed line shown in FIG. 15. A bending angle of the zig-zagbending patterns is roughly 90 degrees, and its bending point isarranged in the almost center of the gate bus line 2. Side surfaces ofthe projection 10 are inclined to the substrate surface.

Also, as shown in FIG. 16 to FIG. 19, dielectric structures 11 areformed on the protection insulating film 7 to be interposed between thegate bus line 2, the drain bus line 5, and the pixel electrode 8respectively.

The dielectric structure 11 and the projection 10 are formed by thefollowing method, for example.

In other words, high-sensitivity negative type resist andlow-sensitivity negative type resist are coated in sequence on theprotection insulating film 7 and the pixel electrode 8. Then, latentimages of the bending patterns are formed on the high-sensitivitynegative type resist by the first exposure. In the first exposure,luminous exposure is set not to expose the low-sensitivity negative typeresist. Then, latent images are formed by irradiating the exposure lightonto regions of the low-sensitivity negative type resist on the gate busline 2 and the drain bus line 5 and their peripheral portions. Forexample, the exposure light is irradiated at least onto an area extendedfrom the gate bus line 2 to an edge of the pixel electrode 8 and an areaextended from the drain bus line 5 to an edge of the pixel electrode 8in one pixel area. The high-sensitivity negative type resist is exposedat the same pattern simultaneously with the exposure of thelow-sensitivity negative type resist. In this case, it is possible tosay that the resists having different sensitivities are substantiallythe same dielectric material.

After this, if the patterns are formed by developing simultaneously thelow-sensitivity negative type resist and the high-sensitivity negativetype resist, the L-shaped dielectric structures 11 shown in FIG. 16 andthe projections 10 having the bending patterns are formed integrally. Inthis case, since the projections 10 is formed of the high-sensitivitynegative type resist while the dielectric structures 11 are formed ofboth the low-sensitivity negative type resist and the high-sensitivitynegative type resist, the dielectric structures 11 become thicker thanthe projections 10.

In the above example, the dielectric structure 11 and the projection 10are formed to have different heights. Since only one layer of the abovephotosensitive resist is needed if they have the same height, the abovestructures can be implemented by the same process as the prior art. Forexample, a film thickness of the dielectric structure 11 and theprojection 10 is set to more than 1 μm.

Such projection 10 and the dielectric structure 11 as well as the pixelelectrode 8 and the protection insulating film 7 are covered with thealignment film (vertical alignment film) 9 formed of resin.

Next, the opposing substrate that opposes to the first glass substrate 1will be explained hereunder.

The opposing substrate consists of the second glass substrate 12 shownin FIG. 17, and then a red (R), green (G), blue (B) color filter film 13is formed on the opposing substrate. Also, a black matrix 14 that has apattern to oppose to the gate bus line 2, the drain bus line 5, and thecapacitive bus lines 3 is formed on the color filter film 13. Inaddition, a transparent common electrode 15 made of ITO is formed on thecolor filter film 13 to cover the black matrix 14.

Projections 16 having zig-zag bending patterns are formed on the commonelectrode 15. As indicated by a chain double-dashed line in FIG. 15, theprojections 16 are arranged on the first glass substrate 1 at positionsin the almost middle between a plurality of projections 10.

The projections 10 on the first glass substrate 1 side and theprojections 16 on the second glass substrate 12 side intersect withedges of the pixel electrodes 8 respectively by an angle of 45 degrees.

In addition, an alignment film (vertical alignment film) 17 for coveringthe projections 16 is formed on the common electrode 15.

The first glass substrate 1 and the second glass substrate 12, formed asabove, are stuck to each other at a predetermined distance to direct thealignment films 9, 17 inward. Then, liquid crystal material 18 havingnegative dielectric anisotropy is filled into a space between thealignment films 9, 17. The liquid crystal molecules in the liquidcrystal material 18 are aligned perpendicularly to the substrate surfaceunder the condition that no voltage is applied between the commonelectrode 15 and the pixel electrode 8. Also, the liquid crystalmolecules are tilted in the direction orthogonal to straight portions ofthe patterns of the projections 10, 16 under the condition that theintermediate voltage is applied between the common electrode 15 and thepixel electrode 8.

In this case, it is desired that the projections 10, 16 are formed ofmaterial having the dielectric constant equivalent to or less than therelative dielectric constant of the liquid crystal material 18.

A first polarizing plate 21 is arranged on an outer surface of the firstglass substrate 1, and a second polarizing plate 22 is arranged on anouter surface of the second glass substrate 12. An arrangement of thefirst polarizing plate 21 and the second polarizing plate 22 iscross-nicol. When the substrate is viewed vertically, polarization axesof the first polarizing plate 21 and the second polarizing plate 22intersect with straight portions of the patterns of the projections 10,16 by an angle of 45 degrees.

In the first embodiment, the structure is formed in which respectivespaces between the pixel electrode 8, the gate bus line 2, and the drainbus line 5 are covered with the dielectric structure 11. Accordingly, agap between the alignment film 9 on the gate bus line 2 and thealignment film 17 on the common electrode 15 becomes narrow, and thus adefining force of the alignment films against the liquid crystalmolecules can be enhanced. In addition, a voltage drop is generatedbetween the gate bus line 2 and the common electrode 15 by thedielectric structure, and also the voltage applied to the liquid crystallayer is lowered.

As results of them, as shown in FIGS. 20A and 20B, the liquid crystalmolecules L over the gate bus line 2 are difficult to tilt since theyreceive the strong vertical alignment definition by the alignment films9, 17. Accordingly, the alignment direction of the liquid crystalmolecules L is hardly affected by the variation of the surroundingelectric field, and thus the variation of the stray capacitance can bereduced.

Also, the relative dielectric constant of the dielectric structure 11 isnot varied and constant such as about 2 to 5, and is smaller than therelative dielectric constant of the liquid crystal in many cases. Forexample, the dielectric structure 11 having the relative dielectricconstant of 3.2 is used. The liquid crystal for the MVA mode has ε(dielectric constant in the perpendicular direction to the liquidcrystal molecules)=3.6, ε//(dielectric constant in the paralleldirection to the liquid crystal molecules)=8.4.

Accordingly, as shown in FIG. 20A and FIG. 20B, the capacitance Cgcbetween the pixel electrode 8 and the gate bus line 2 and thecapacitance Cds between the pixel electrode 8 and the drain bus line 5are seldom changed. Further, because the voltage drop is generated bythe dielectric structure 11, the voltage applied to the liquid crystallayer on the gate bus line 2 is also lowered. As a result, the straycapacitances between the bus lines can be reduced and the straycapacitance between the bus line and pixel electrode can be reduced.

With the above, since the variation of the stray capacitances becomesextremely small and the constant pixel potential can be always obtained,the aperture ratio can be increased by reducing the width of thecapacitive bus line 3. In addition, when the potential of the pixelelectrode is kept constant, generation of the flicker can be prevented.

For example, in the liquid crystal display panel employing the abovestructure, the variation of the common voltage is less than 10 mV andalso the flicker rate can be improved below 3%, which is reduced below ahalf of the flicker rate in the prior art. Accordingly, yield of theliquid crystal display panel can be improved.

In the above first embodiment, since formation of the dielectricstructures 11 and formation of the projections 10 can be performed bythe same step, the above liquid crystal display device can be formed tohardly increase the number of processes rather than the prior art.

In this case, the above dielectric structure 11 may be formed toprotrude to such extent that it overlaps slightly with the pixelelectrode 8.

Second Embodiment

In the first embodiment, only spaces between the gate bus lines 2 andthe drain bus lines 5 for driving the pixel electrodes and the pixelelectrodes 8 are covered with the dielectric structures 11 in one pixelarea.

Arrangement areas of the dielectric structures are not limited to theabove. For example, as shown in FIG. 21, dielectric structures 11 a maybe provided between neighboring pixel electrodes 8. In such structure, aperipheral area of the pixel electrode 8 and the gate bus line 2 and thedrain bus line 5 are covered with the dielectric structure 11 a.

The flicker rate can be improved by employing such structure rather thanthe first embodiment.

Further, only spaces between the gate bus line 2 and the pixel electrode8 may be covered with the dielectric structure, or only spaces betweenthe drain bus line 5 and the pixel electrode 8 may be covered with thedielectric structure. According to these structures, the effect by thedielectric structures 11, 11 a shown in FIG. 16 or FIG. 21 cannot beachieved, but both the common voltage variation and the flicker rate aregood.

Furthermore, in FIG. 15, the dielectric structure may be formed only inintersecting areas of the gate bus lines 2 and the projections 11 andtheir neighboring areas. Otherwise, the dielectric structure may beformed only in intersecting areas of the drain bus lines 5 and theprojections 11 and their neighboring areas. According to thesestructures, such effects can be derived that the influence of the chargeof the projections 10 can be reduced rather than the first embodimentand also the alignment change between the gate bus lines 2 and the pixelelectrodes 8 in the neighborhood of the projections 10 can besuppressed. In this case, the flicker rate cannot be so improved incontrast to the dielectric structures shown in FIG. 16 or FIG. 21, butboth the common voltage variation and the flicker rate are good.

The above descriptions are all directed to the embodiments in which thedielectric structures are formed on the first glass substrate 1 side,but the dielectric structures may be formed on the second glasssubstrate (opposing substrate) 12 side. For example, as shown in FIG.22, such a structure may be employed that dielectric structures 11 b areformed on the common electrodes 15 at positions to which the dielectricstructures 11, 11 a shown in FIG. 16 or FIG. 21 oppose, and then thealignment film 17 is formed thereon. In this case, an effect for fixingperfectly the capacitance Cgs between the gate and the pixel electrodeand the capacitance Cds between the drain and the pixel electrode cannotbe achieved, but an effect for suppressing the alignment change to thelowest minimum can be expected by the narrower cell gap effect. Suchnarrower cell gap effect remarkably appears by setting a thickness ofthe dielectric structure 11 b to more than 1 μm, like the firstembodiment.

Also, in the above examples, the dielectric structure is formed only bythe resist, for example. In addition to this, as shown in FIG. 23,overlapped portions may be utilized as a part of the dielectricstructure on the opposing substrate side by overlapping red, green, bluecolor filters 13R, 13G, 13B mutually on the boundary portions betweenthe pixel areas respectively. Accordingly, the liquid crystal can beremoved from the areas in which the alignment change is suppressed inthe area other than the pixel electrodes 8, and thus change in thecapacitance due to the alignment change is not generated. As a result,the similar effect to the first embodiment can be achieved.

As the areas in which the differently-colored color filters 13R, 13G,13B are overlapped with each other, only the areas between the gate buslines 2 and the pixel electrodes 8 or the areas between the drain buslines 5 and the pixel electrodes 8 may be considered. In this case, thedielectric structure may be formed on the first glass substrate 1 so asto oppose to the overlapped portions of the differently-colored colorfilters 13R, 13G, 13B.

As shown in FIG. 23, a dielectric structure 11 c may be formed on theoverlapped portions of the red, green, blue color filters 13R, 13G, 13B,or may be omitted. However, in the case that the structure shown in FIG.23 is employed, spacers (spherical or cylindrical spacers) interposedbetween the substrates can be omitted if the overlapped portions of thecolor filters 13R, 13G, 13B and the dielectric structures 11 c formedthereon are employed as struts to maintain the cell gap.

In this case, the above dielectric structures may be formed on both thesecond glass substrate 12 side and the first glass substrate 1 side.Then, the cell gap may be maintained by the vertically-engageddielectric structures. In addition, the variation of the common voltageof less than 10 mV and the flicker rate of less than 2% can be achievedby employing the optimum structure.

The structure in which at least one of the projection 10 on the firstglass substrate 1 side and the projection 16 on the second glasssubstrate 12 side is not provided in the neighborhood of the areaintersecting with the gate bus line 2, the structure in which at leastone of them is not provided in the neighborhood of the area intersectingwith the drain bus line 5, or the structure in which at least one ofthem is not provided in areas other than the pixel electrode 8 may beemployed.

In the first embodiment and the second embodiment, the projections areemployed as the means for defining the alignment direction of the liquidcrystals. The slits may be formed on at least one of the pixel electrodeand the common electrode in place of the projections.

The dielectric structure shown in the first embodiment and the secondembodiment may be applied to not only the MVA mode liquid crystaldisplay device but also other liquid crystal display devices. In thiscase, the slits formed in the pixel electrode 8 or the common electrode15 may be used instead of either one of the projections 10 on the firstglass substrate 1 side and the projections 16 on the second glasssubstrate 12 side.

As described above, according to the present invention, since thedielectric structures are arranged in the areas between the gate buslines (first bus lines) and the pixel electrodes, both intersect witheach other, or the areas between the drain bus lines (second bus lines)and the pixel electrodes, variation of the stray capacitance betweenthem can be suppressed by fixing the dielectric constant between thepixel electrodes and the bus lines by the dielectric structures. Also,since the dielectric structures are also formed on the bus lines, thethickness of the liquid crystal layer in the dielectric structures canbe reduced. As a result, the liquid crystal molecules in the liquidcrystal layer is hardly moved from the vertical alignment and thus thevariation of the stray capacitance can be extremely reduced. Besides,since a component of the stray capacitance over the bus lines fixed bythe dielectric structures is increased, the variation of the straycapacitance can be reduced.

As mentioned above, since the pixel potential becomes constant bysuppressing the variation of the stray capacitance, generation of theflicker can be prevented. In addition, the aperture ratio can beenhanced by reducing the width of the capacitive bus line to suppressthe variation of the capacitance.

Third Embodiment

FIG. 24 is a sectional view showing a third embodiment of the presentinvention, that has the similar structure to the first embodiment otherthan the pixel electrode, the projection, and the dielectric structure.In FIG. 24, same references as those in FIG. 17 denote same elements.

In FIG. 24, the gate bus line 2 and the capacitive bus line 3 are formedon the first glass substrate (TFT substrate) 1. Also, like the firstembodiment, the drain bus line 5 and the thin film transistor (TFT) 6are formed on the gate insulating film 4 that covers these bus lines 2,3. The drain bus line 5 and the thin film transistor (TFT) 6 are coveredwith the protection insulating film 7, and then a pixel electrode 30 isformed on the protection insulating film 7. As shown in FIG. 25, thepixel electrode 30 is arranged in an area that is surrounded by the gatebus line 2 and the drain bus line 5.

Slits 30 a, 30 b that extend like the V-shape from edge areas of thepixel electrode 30 existing on the capacitive bus line 3 are formed inthe pixel electrode 30. Slits 30 c, 30 d are formed in parallel with theslits 30 a, 30 b in the pixel electrode 30. The slit width is 10 μm, forexample.

These slits (domain defining means) 30 a to 30 d divide the pixelelectrode 30 into five areas. These areas are electrically connectedmutually by connecting portions 30 n that separate the slits 30 a to 30d into plural areas.

In addition, connecting portions 30 e used to connect electrically fiveareas divided by the slits 30 a to 30 d are formed within apredetermined width w1, e.g., within a range of 4 μm, from the edge ofthe pixel electrode 30. End portions of the slits 30 a to 30 d areseparated by the connecting portions 30 e.

The connecting portions 30 e acts as an alignment controlling means forforming an alignment singular point of s=−1. As shown in FIGS. 26A and26B, according to the alignment controlling means having the alignmentsingular point of s=−1, the liquid crystal molecules L in one directionout of two orthogonally intersecting directions around a point O arealigned to direct to the point O while the liquid crystal molecules L inthe other direction are aligned to direct to the opposite side Lo thepoint O. Also, the liquid crystal molecules L inclined to thesedirections by 45 degrees are directed to different directionsrespectively.

In this case, as shown in FIG. 26B, according to the alignmentcontrolling means forming an alignment singular point of s=+1 describedin following embodiments, all liquid crystal molecules L around thepoint O are aligned to direct to the point O.

As shown in FIG. 24, the above-mentioned pixel electrode 30 is connectedto the TFT 6 and is covered with the alignment film 9.

Like the first embodiment, as shown in FIG. 24, the color filter 13, theblack matrix 14, the common electrode 15, dielectric projections (domaindefining means) 31, and the alignment film 17 are formed in sequence onthe surface of the second glass substrate (opposing substrate) that isarranged to oppose to the pixel electrode 30.

As the alignment films 9, 17 on the first and second glass substrates 1,12, JALS-684 (product name manufactured by JSR Inc.), for example, isemployed.

Like the first embodiment, as indicated by a chain double-dashed line inFIG. 25, the dielectric projections 31 are formed in a zig-zag fashionto oppose to positions that pass through between the slits 30 a to 30 dof the pixel electrode 30. The projections 31 are formed byphotosensitive acrylic resin PC-335 (product name manufactured by JSRInc.), for example. Patterns of the projections 31 are formed by coatingthe photosensitive acrylic resin on the substrate by virtue of spincoating, then baking the resin at 90° C. for 20 minutes, thenirradiating selectively the ultraviolet rays by using a photo mask, thendeveloping the resin by an organic alkaline liquid developer (TMAHO, 2wt %), and then baking the resin at 200° C. for 60 minutes. A width ofthe projection 31 is 10 μm and a height of the projection 31 is 1.5 μm.

A liquid crystal panel is formed by sticking the first glass substrate 1and the second glass substrate 12 having the above structure togetherand then injecting the liquid crystal into a space between them. In thiscase, MJ961213 (product name manufactured by Merck Inc.) is employed asthe liquid crystal material.

In the liquid crystal display device having the above configuration, theslits 30 a to 30 d of the pixel electrode 30 acting as the domaindefining means are not formed at the edges of the pixel electrode 30 andits neighboring area, and the alignment singular points are formedthere. Accordingly, difference of the domain states between the whitemonitored when the display of the pixel is changed from the black to thewhite and the white monitored when the display of the pixel is changedfrom the half tone to the white can be reduced to an unobtrusive level,so that the domain change can be reduced up to a undistinguishable levelas the residual image.

Here, the domain defining means of the liquid crystal molecules is notlimited to the linear slits in the pixel electrode. For example, thestructure may be employed in which the linear dielectric projectionslike the first embodiment are provided in place of the slits on thepixel electrode. In this case, if the separated portions that are notintersected with the edges of the pixel electrode are formed as theprojections, the alignment singular point of s=−1 is formed at the edgeportion of the pixel electrode on the prolonged line of the projection.

Also, in place of forming the projections 31 on the common electrode 15being formed on the opposing substrate 12 side, the slits may be formedin the common electrode 15.

Fourth Embodiment

In the third embodiment, the alignment singular point of s=−1 is formedat the intersecting portions between the structures or the slits formedon the pixel electrode and the edges of the pixel electrode. Incontrast, in a fourth embodiment, such a configuration will be explainedhereunder that the alignment singular point of s=+1 is formed at theintersecting portions between the structures or the slits formed on thesubstrate opposing to the substrate having the pixel electrode and theedges of the pixel electrode.

FIG. 27 is a plan view showing the pixel area of the liquid crystaldisplay device according to the fourth embodiment of the presentinvention. FIG. 28 is a sectional view taken along a VII—VII line inFIG. 27.

In FIG. 27, slits 33 a, 33 b that extend like the V-shape from the edgeareas of the pixel electrode 33 existing on the capacitive bus line 3are formed in the pixel electrode 33. Slits 33 c, 33 d are formed inparallel with these slits 33 a, 33 b in the area of the pixel electrode33 near the gate bus line 2. The slit width is 10 μm, for example. Theslits 33 a to 33 d are also formed on the edges of the pixel electrode33. The slits 33 a to 33 d are separated by the connecting portions 33e.

Also, as shown in FIG. 27 and FIG. 28, in the dielectric projections(structures) 34 formed on the opposing substrate 12 side, the alignmentsingular point in the neighborhood of the edge of the pixel electrode 33is formed as s=+1 by setting a portion 34 a opposing to the edge of thepixel electrode 33 higher than other areas. A height of the portion ofthe projection 34 to oppose to the edge of the pixel electrode 33 is setto 2.5 μm, and a height of other portion is set to 1.5 μm.

The projections 34 are formed of the same constituent material as theprojections 31 in the third embodiment. First, the pattern of theprojections 34 are formed on the common electrode 15 to have a height of1.5 μm, and then projections 34 a of 1.0 μm height is selectivelystacked in areas opposing to the edges of the pixel electrode 33.

In this manner, since a portion of the projection 34 on the opposingsubstrate 12 side, that opposes to the edge of the pixel electrode 33,is set higher than other portions, the alignment singular point of s=+1is formed on the edge of the pixel electrode 33, as shown in FIG. 27 andFIG. 28. As a result, the influence of the alignment of the liquidcrystal molecules L at the edge of the pixel electrode 33 upon theliquid crystal molecules at the inside of the pixel electrode 33 can beprevented by the alignment singular point, so that generation of theresidual images caused when the display is changed from the half tonedisplay to the white display can be prevented.

In the case that the slits are formed in the common electrode 15 on theopposing substrate 12 in place of the projections 34, the similaroperation and effect can be achieved if such slits are divided atportions opposing to the pixel electrode 33.

By the way, a combination of the TFT substrate in the third embodimentand the opposing substrate in the fourth embodiment can provide the beststructure. More particularly, the preferable structure can be obtainedby separating the linear slits or the linear projections formed on theTFT substrate side not to intersect with the edge of the pixel electrodeand also separating the linear slits in the common electrode on thecommon electrode side not to intersect with the pixel electrode orforming portions of the linear projections, that oppose to the edge ofthe pixel electrode, on the common electrode side thicker than otherportions.

Fifth Embodiment

In the third embodiment, bending portions of the slits formed on thepixel electrode, i.e., intersecting portions of prolonged lines of theslits in two directions are formed to coincide with the edge of thepixel electrode. In this case, such intersection points may be shiftedinward from the edge of the pixel electrode.

FIG. 29 is a plan view showing a pixel electrode and its neighboringarea of a liquid crystal display device according to a fifth embodimentof the present invention.

In FIG. 29, a bending portion 35 b of a slit 35 a opened in the pixelelectrode 35 is formed to retreat inward from the edge of a pixelelectrode 35. For example, a distance from the bending portion 35 b tothe edge of the pixel electrode 35 is set to 4 μm and a width of theslit 35 a is set to 10 μm.

Also, like the first embodiment, projections 36 are formed on theopposing substrate 12 side at positions passing through between theslits 35 a.

According to this, the influence of the electric field by the edge ofthe pixel electrode 35 upon the, bending portion 35 b of the slit 35 acan be reduced and thus generation of the residual images can besuppressed.

In FIG. 29, the structure in which the slits are formed in the pixelelectrode 35 is employed. In the event that the dielectric projectionsare formed on the pixel electrode 35 instead of the slits like the firstembodiment, the influence of the electric field by the edge of the pixelelectrode 35 upon the bending portion of the projections can be reducedand thus generation of the residual images can be suppressed if thebending portions of the projections are formed to retreat inward fromthe edge of the pixel electrode.

Also, as shown in FIG. 30, for example, as the shape of a dielectricprojection 37 formed as the alignment controlling means on the opposingsubstrate 12, if the projection 37 is bent in the area opposing to thepixel electrode such that the bending portion is arranged to be shiftedinward from the edge of a pixel electrode 38, the influence of theelectric field by the edge of the pixel electrode 38 upon the bendingportion can be reduced and thus the residual image suppressing effectcan be achieved. In this case, for example, a width of the projection 37is set to 10 μm and a distance from the bending portion to the edge ofthe pixel electrode 38 is set to 4 μm.

It may be considered that the slits are formed in the common electrode15 shown in FIG. 24 as the alignment controlling means on the opposingsubstrate 12 in place of the dielectric projections 37. However, sincenormally the color filter 13 is formed under the common electrode 15, itis not preferable from aspects of precision and reliability to form theslit in the common electrode 15.

In FIG. 30, because the bending portions (intersecting portions) of theslits 38 a, 38 b formed on the pixel electrode 38 to extend in twodirections are positioned on the outside of the pixel electrode 38, theinfluence of the electric field by the edge of the pixel electrode 38upon the bending portions can be eliminated. Accordingly, generation ofthe alignment state that is different from the essential alignmentcontrol and generated by the projections or the slits can be reduced,and also the residual images caused when the display is changed from thehalf tone display to the white display can be eliminated.

Sixth Embodiment

FIG. 31A is a plan view showing a pixel electrode and its neighboringarea of a liquid crystal display device according to a sixth embodimentof the present invention.

In FIG. 31A, such a structure is employed that intersecting portions ofa first slit 40 a and a second slit 40 b, that are formed like a V-shapenear the center of a pixel electrode 40, are connected via a slit 40 e,that is formed in parallel with the edge of the pixel electrode 40, at aposition inner than the edge. A distance of a clearance 40 g between theslit 40 e and the edge of the pixel electrode 40 is set to 4 μm, forexample.

Also, third and fourth slits 40 c, 40 d are formed in the pixelelectrode 40 near the gate electrode 2.

These first to fourth slits 40 a to 40 d are separated by connectingportions 40 f at plural portions. Therefore, the pixel electrode 40 isdivided into five areas A to E by the first to fourth slits 40 a to 40d, and these areas A to E are electrically connected by the connectingportions 40 f.

The area C divided by the first and second slits 40 a, 40 b is opposedelectrically and structurally to the storage capacitance formingelectrode (capacitive bus line) 3. Also, at least two electricalconnecting paths are opposed electrically to the storage capacitanceforming electrode 3.

Accordingly, as shown in FIG. 31B, the area B and the area D of thepixel electrode 40 are connected via two routes of a route B-C-D and aroute B-D. Then, if the area C of the pixel electrode 40 and the storagecapacitance forming electrode 3 are short-circuited, four areas A, B, D,E of the pixel electrode 40 can be electrically connected via theexisting connecting portion 40 f and the clearance 40 g by disconnectingthe electrical connections of B-C and C-D by the laser irradiation ontothe connection portion 40 f. Therefore, it is possible to drive theliquid crystal molecules in most portions other than the area C.

Such pixels that can be driven in areas other than such area C haveslightly different display characteristic in contrast to the normalstate in which the area C of the pixel electrode 40 and the storagecapacitance forming electrode 3 are not short-circuited. However, sincesuch different display can be improved up to a level to clear thedisplay defect standard according to the number of defective pixels andthe generation location, the improvement in yield of the TFT substratecan be achieved. This can be attained by such a structure that pluralareas of the pixel electrode divided by the slits are connected the edgeportion of the pixel electrode, whereby this respect is different fromthe structure in the prior art.

In this case, if the pixel electrode 40 is divided into at least threeareas by the first and second slits 40 a, 40 b, for example, such yieldimproving effect can be attained.

Next, change of the domain on the slits when the present invention isapplied will be explained with reference to FIGS. 32A and 32B hereunder.

First, as shown in FIG. 32A, when the display is changed from the blackdisplay to the white display, the number of domains divided by theconnecting portions on the slit 40 a is eight such as {circle around(1)} to {circle around (8)}. Also, according to FIG. 32A, the domains{circle around (8)} and {circle around (9)} are increased in numberrather than the prior art shown in FIG. 10A. This is because thesingular point s=−1 of the alignment vector is formed at the edge of thepixel electrode.

Then, as shown in FIG. 32B, when the display is changed from the blackdisplay to the white display via the half tone display, the domains{circle around (6)} and {circle around (8)} are connected and thus thedomain {circle around (7)} disappears. In other words, the change ofdomains on the slits can be suppressed at a very small level rather thanFIG. 10A in the neighborhood of the edge of the pixel electrode.

According to the present invention, in the display mode in which theliquid crystal molecules alignment is controlled by the structures orthe slits provided on the substrate, the improvement of the responsecharacteristic can be achieved by forming the alignment singular points,at which the liquid crystal molecules become s=−1 or s=+1, on theintersecting portions between the prolonged lines of the structures orthe slits and the pixel electrode, etc.

Besides, in the present invention, two routes, i.e., the route passingthrough the area in which the storage capacitance forming electrode andthe capacitance are formed and the route not passing through such areaare provided as the electrical connecting paths of the pixel electrode.Therefore, if the electric short-circuit between the storage capacitanceforming electrode and the pixel electrode is generated, the area inwhich the capacitance is formed can be disconnected electrically fromother areas, and thus other areas can be employed as the area in whichthe liquid crystal molecules can be driven. As a result, the improvementin yield of the TFT substrate manufacture can be achieved.

Seventh Embodiment

Next, a liquid crystal display device according to a seventh embodimentof the present invention will be explained with reference to FIG. 33 toFIG. 36 hereunder.

FIG. 33 is a plan view showing an MVA liquid crystal display deviceaccording to the seventh embodiment. A plurality of gate bus lines 205are formed to extend along the row direction (lateral direction) in FIG.33. A capacitive bus line 208 extending in the row direction is arrangedbetween two neighboring gate bus lines 205. The gate bus lines 205 andthe capacitive bus lines 208 are covered with an insulating film. Aplurality of drain bus lines 207 that extend along the column direction(longitudinal direction) in FIG. 33 are arranged on this insulatingfilm.

TFTs 210 are provided to correspond to intersecting portions between thegate bus line 205 and the drain bus line 207. A drain region of the TFT210 is connected to the corresponding drain bus line 207. The gate busline 205 is also used as a gate electrode of the corresponding TFT 210.

The drain bus lines 207 and the TFTs 210 are covered with an interlayerinsulating film. A pixel electrode 212 is arranged in an area surroundedby two gate bus lines 205 and two drain bus lines 207. The pixelelectrode 212 is connected to a source region of the corresponding TFT210.

Auxiliary capacitive branch lines 209 branched from the capacitive buslines 208 extend along the edge of the pixel electrode 212. Thecapacitive bus lines 208 and the auxiliary capacitive branch lines 209constitute an auxiliary capacitance between the pixel electrodes 212.The potential of the capacitive bus lines 208 is fixed at any potential.

When the potential of the drain bus line 207 is varied, the potential ofthe pixel electrode 212 is also varied by the capacitive coupling due tothe stray capacitance. In the configuration in FIG. 33, since the pixelelectrode 212 is connected to the capacitive bus lines 208 via theauxiliary capacitance, variation in the potential of the pixel electrode212 can be reduced.

TFT substrate side projections 217 and CF substrate side projections 218are formed on the opposing surfaces of the TFT substrate and theopposing substrate (the opposing substrate is called a color filter (CF)substrate in some cases since normally the color filter is provided onthe opposing substrate side) along zig-zag patterns extending along thecolumn direction respectively. The TFT substrate side projections 217are arranged at an equal distance in the row direction, and bendingpoints are positioned on the gate bus line 205 and the capacitive buslines 208. The CF substrate side projection 218 has an almost congruentpattern to the TFT substrate side projection 217 and is arranged in thealmost middle of two neighboring TFT substrate side projections 217. Theprojections 217 and 218 have a width of about 10 μm respectively.

The polarizing plates are arranged on both sides of the liquid crystalcell. The polarizing plates are cross- nicol-arranged such that theirpolarization axes intersect with straight portions of the projections217, 218 by an angle of 45 degrees.

FIG. 34 is a sectional view showing the TFT portion taken along aVIII—VIII line in FIG. 33, and FIG. 35 is a sectional view showing thepixel electrode portion taken along a IX—IX dot-dash line in FIG. 33.The TFT substrate 235 and the opposing substrate 236 are arranged inparallel at a distance. Liquid crystal material 229 is filled betweenthe TFT substrate 235 and the opposing substrate 236. The liquid crystalmolecules in the liquid crystal material 229 have the negativedielectric anisotropy.

As shown in FIG. 34, the gate bus lines 205 are formed on the opposingsurface of the glass substrate 201. The gate bus lines 205 are formed bydepositing an Al film of 100 nm thickness and a Ti film of 50 nmthickness by virtue of the sputtering and then patterning these twolayers. The etching of the Al film and the Ti film is carried out by theRIE using a mixed gas of BCl₃ and Cl₂.

A gate insulating film 240 is formed on the glass substrate 201 to coverthe gate bus lines 205. The gate insulating film 240 is formed of an SiNfilm of 400 nm thickness, and is formed by the PE-CVD method. An activearea 241 is arranged on a surface of the gate insulating film 240 tocross the gate bus line 205. The active area 241 is formed of an undopedamorphous Si film of 30 nm thickness, and is formed by the PE-CVDmethod. A surface of the active area 241 over the gate bus lines 205 iscovered with a channel protection film 242. The channel protection film242 is formed of an SiN film of 140 nm thickness. The channel protectionfilm 242 is patterned to cover the channel region of the TFT 210 in FIG.33.

Formation of the channel protection film 242 is carried out by thefollowing method. First, a surface of the SIN film formed on the overallsurface of the substrate is covered with the photoresist film. An edgeof the resist pattern parallel to the row direction in FIG. 33 can bedefined by exposing the photoresist from a back surface of the glasssubstrate 201 using the gate bus lines 205 as a photo mask. An edge ofthe resist pattern parallel to the column direction in FIG. 33 can bedefined by exposing the photoresist using the normal photo mask.

After the photoresist film is developed, the SiN film is patterned byetching the photoresist film using the buffer hydrofluoric acid etchant.In this case, the SiN film may be patterned by the RIE using a fluorinegroup gas. After the SiN film is patterned, the resist pattern isremoved. The channel protection film 242 is formed by the stepsperformed until now.

A source electrode 244 and a drain electrode 246 are formed on the uppersurface of the active area 241 on both side areas of the channelprotection film 242 respectively. Both the source electrode 244 and thedrain electrode 246 have a laminated structure which is formed bylaminating an n⁺-type amorphous Si film of 30 nm thickness, a Ti film of20 nm thickness, an Al film of 75 nm thickness, and a Ti film of 80 nmthickness in sequence. The TFT 210 consists of the gate bus line 205,the gate insulating film 240, the active area 241, the source electrode244 and the drain electrode 246.

The active area 241, the source electrode 244 and the drain electrode246 are patterned by using one etching mask. The etching of these filmsis carried out by the RIE using the mixed gas of BCl₃ and Cl₂. At thistime, the channel protection film serves as an etching stopper over thegate bus line 205.

The pixel electrode 212 is formed on the protection insulating film 248.The pixel electrode 212 is formed of an ITO film of 70 nm thickness, andis connected to the source electrode 244 via a contact hole 250 providedin the protection insulating film 248. Formation of the ITO film isperformed by the DC magnetron sputtering. The patterning of the ITO filmis performed by the wet etching using the oxalic acid group etchant. Thepixel electrode 212 and the protection insulating film 248 are coveredwith an alignment film 228.

Then, a configuration of the opposing substrate 236 will be explainedhereunder. A color filter 251 is formed on the opposing surface of theglass substrate 227. A light shielding film 252 made of Cr, etc. isformed on a surface of the color filter 251 in an area opposing to theTFT 210. A common electrode 254 made of ITO is formed on the surface ofthe color filter 251 to cover the light shielding film 252. A surface ofthe common electrode 254 is covered with the alignment film 228.

The pixel electrode portion shown in FIG. 35 will be explainedhereunder. The capacitive bus line 208 is formed on the surface of theglass substrate 201. The capacitive bus line 208 is formed by the samesteps as those applied to the gate bus line 205 shown in FIG. 34. Thegate insulating film 240 and the protection insulating film 248 areformed on the surface of the glass substrate 201 to cover the capacitivebus line 208. The pixel electrode 212 is formed on the surface of theprotection insulating film 248.

The TFT substrate side projections 217 are formed on the surface of thepixel electrode 212. The TFT substrate side projections 217 are formedby coating the polyimide-based photoresist and then patterning theresist film, as shown in FIG. 33. The surfaces of the TFT substrate sideprojections 217 and the pixel electrodes 212 are covered with thealignment film 228.

The color filter 251 is formed on the opposing surface of the glasssubstrate 227 opposing to the TFT substrate 235. The light shieldingfilm 252 is formed on a part of the surface of the color filter 251. Thecommon electrode 254 is formed on the surface of the color filter 251 tocover the light shielding film 252. The CF substrate side projections218 are formed on the surface of the common electrode 254. The CFsubstrate side projections 218 are formed by the same method as theformation of the TFT substrate side projections 217. The surfaces of theCF substrate side projections 218 and the common electrode 254 arecovered with the alignment film 228.

In order to execute the image display, a constant common voltage isapplied to the common electrode 254 and a image signal whose polarity isinverted frame by frame is applied to the pixel electrode 212. If thevoltage applied to the liquid crystal layer when the pixel electrode 212is positive for the common electrode 254 is equal to that applied to theliquid crystal layer when the pixel electrode 212 is negative for thecommon electrode 254, the transmittance obtained when the pixelelectrode 212 has a positive polarity becomes equal to that obtainedwhen the pixel electrode 212 has a negative polarity. Thus, the stabledisplay can be derived.

Compensating members 221 having the refractive anisotropy are formed ona surface of the glass substrate 201 on the opposite side to theopposing surface. If viewed along the normal direction of the substrate,the compensating members 221 are formed along the edge of the TFTsubstrate side projections 217 or to overlap substantially with theirinclined surfaces. The liquid crystal molecules in the neighborhood ofthe edges of the TFT substrate side projections 217 are tilted againstthe substrate surface by the influence of the inclined surfaces of theprojections 217. The tilt has the double refraction effect on the lighttransmitted in the thickness direction of the liquid crystal layer. Thecompensating members 221 have the refractive anisotropy to reduce thisdouble refraction effect. Similar compensating members 222 are formed onthe surface on the opposite side to the opposing surface so as tocorrespond to the projections 218.

In the dark state, the double refraction effect caused by the liquidcrystal layer in the neighborhood of the edges of the projections 217,218 is canceled by the double refraction effect caused due to therefractive anisotropy of the compensating members 221 and 222.Therefore, leakage lights in the neighborhood of the edges of theprojections 217, 218 in the dark state can be reduced.

In order to sufficiently compensate the double refraction effect whenviewed from the oblique direction, it is preferable that the glasssubstrates 101, 227 should be formed as thin as possible. The case wherethe glass substrate is employed is explained with reference to FIG. 34and FIG. 35. However, even if a thin film substrate of about severaltens μm thickness is employed in place of the glass substrate, thedouble refraction effect can be sufficiently compensated in the obliquedirection.

Next, a method of manufacturing the compensating members 222 shown inFIG. 35 will be explained with reference to FIG. 36 hereunder. A methodof manufacturing the compensating members 221 on the TFT substrate 235side is similar to a method explained in the following.

The transparent electrode layer 260 formed of ITO to have a thickness of100 nm is formed on the surface of the glass substrate 227, that is onthe opposite side to the surface on which the projections 218 areformed. As shown in FIG. 33, the projection 218 contains locally aportion parallel to the first direction and a portion parallel to thesecond direction perpendicular to the first direction. First, all areasof the surface of the transparent electrode layer 260 are rubbed in thefirst direction.

Then, the area of the projection 218, in which portions being parallelto the first direction are aligned, is masked by the resist pattern.Then, areas not covered with the resist pattern are rubbed in the seconddirection. After this, the resist pattern is removed. In other words,the rubbing direction becomes locally parallel to the extendingdirection of the projections 218.

A ultraviolet UV curable liquid crystal layer 261 of 2.5 μm thickness isformed by coating the material, that is obtained by adding thephotopolymerization initiator of 1 wt % into the UV curable liquidcrystal material, on the surface of the transparent electrode layer 260.As the UV curable liquid crystal material, for example, monoacrylateexpressed by the following chemical formula (1) may be employed.CH₂═CHCOO—C₆H₄—C₆H₄—C₃H₇  (1)

This monoacrylate exhibits a liquid crystal phase at the roomtemperature. The phase transition temperature Tni of the liquid crystalmaterial is 52° C., the refractive anisotropy Δn of the liquid crystalmaterial is 0.160, and the dielectric anisotropy Δε of the liquidcrystal material is 0.7. The liquid crystal molecules in the UV curableliquid crystal layer 261 are aligned such that their director becomesparallel to the rubbing direction of the transparent electrode layer260.

A transparent electrode plate 262 is arranged on the UV curable liquidcrystal layer 261 to come into contact with its surface. A rectangularwave voltage having a peak value 60 V is applied between the transparentelectrode layer 260 and the transparent electrode plate 262. The liquidcrystal molecules in the UV curable liquid crystal layer 261 are tiltedby the voltage application. A tilt angle depends upon the appliedvoltage.

The ultraviolet rays are irradiated onto the UV curable liquid crystallayer 261 via a photo mask 263 under the condition that the voltage isapplied. The light shielding pattern is formed in the areas of thesurface of the photo mask 263, except the areas corresponding to theinclined surfaces of the projections 218. The intensity of theirradiated ultraviolet rays is 0.8 mW/cm², for example.

The polymerization reaction occurs in the portions of the UV curableliquid crystal layer 261, that correspond to the inclined surfaces ofthe projections 218, according to the irradiation of the ultravioletrays. Then, the UV curable liquid crystal material that has not beenpolymerized is removed by cleaning the substrate. In this manner, thecompensating members 222 shown in FIG. 35 are formed.

The compensating members 222 formed in the above conditions have therefractive anisotropy that has the direction parallel to the projections218 as the lag phase axis. The retardation is about 10 nm. Therefractive anisotropy Δn of the compensating members 222 can be changedby changing the voltage applied between the transparent electrode layer260 and the transparent electrode plate 262.

Eighth Embodiment

Next, a liquid crystal display device according to an eighth embodimentwill be explained with reference to FIG. 37 and FIG. 38 hereunder. Inthe liquid crystal display device according to the eighth embodiment,the compensating members 221, 222 shown in FIG. 35 in the seventhembodiment are not provided. The double refraction effect of the liquidcrystal layer can be compensated by the refractive anisotropy of theprojection itself. Other configuration is similar to the configurationof the liquid crystal display device according to the seventhembodiment.

FIG. 37 is a sectional view showing a projection 218 and itsneighborhood of an MVA liquid crystal display device according to theeighth embodiment. In this case, a projection on the TFT substrate 235side has the structure similar to that of the projection 218 shown inFIG. 37.

The projection 218 is separated into edge portions 218 a positioned inthe peripheral areas, and an inner portion 218 b positioned between theedge portions 218 a on both sides. The edge portions 218 a has therefractive anisotropy, but the inner portion 218 b has hardly therefractive anisotropy. The double refraction effect due to tilted liquidcrystal molecules 229 a in the neighborhood of the edge portions 218 acan be compensated by the double refraction effect due to the refractiveanisotropy of the edge portions 218 a.

Then, a method of manufacturing the projections of the liquid crystaldisplay device according to the eighth embodiment will be explained withreference to FIG. 38 hereunder. The surface of the common electrode 254is rubbed in the direction parallel to the projections. A UV curableliquid crystal layer 265 of 1.5 μm is formed on the surface of thecommon electrode 254. The UV curable liquid crystal layer 265 is formedof the same material as the UV curable liquid crystal layer 261 shown inFIG. 36 in the seventh embodiment.

An electric plate 266 is arranged to substantially come into contactwith the surface of the UV curable liquid crystal layer 265. Atransparent electrode pattern 267 that corresponds to an area serving asthe inner portions 218 b of the projections and another transparentelectrode pattern 268 arranged on both sides of the transparentelectrode pattern 267 are provided on the electric plate 266.

A rectangular wave voltage e1 is applied between the common electrode254 and the transparent electrode pattern 267, and a rectangular wavevoltage e2 is applied between the common electrode 254 and thetransparent electrode pattern 268. The voltage e1 is higher than thevoltage e2. The large electric field is generated in the area serving asthe inner portions 218 b of the UV curable liquid crystal layer 265 inthe thickness direction. Therefore, the liquid crystal molecules in thisportion are aligned substantially perpendicularly to the substratesurface. Since only the relatively small electric field is generated inthe area serving as the inner portions 218 b, the liquid crystalmolecules in this portion are tilted to the substrate surface.

Under this condition, the ultraviolet rays are irradiated onto the areaof the UV curable liquid crystal layer 265, in which the projections areto be formed, via the photo mask 269. The polymerization reaction iscaused in the area of the UV curable liquid crystal layer 265, in whichthe projections are to be formed, by the irradiation of the ultravioletrays. After the irradiation of the ultraviolet rays, the UV curableliquid crystal material in which the polymerization is not caused isremoved by cleaning the substrate. In this manner, the projections shownin FIG. 37 are formed.

Projections 217 on the TFT substrate 235 are manufactured by the similarmethod. In this case, the pixel electrodes that are separated everypixel are formed on the TFT substrate 235. Therefore, after all TFTs arebrought into their conductive state, the rectangular wave voltage isapplied between the drain bus line and the electrode plate 266. Sincethe TFTs are set to their conductive state, the rectangular wave voltageis applied to all pixel electrodes, and the electric field is generatedin the UV curable liquid crystal layer.

As described above, according to the present invention, the doubleretraction effect of the liquid crystal layer due to the tilt of theliquid crystal molecules in the neighborhood of the edges of theprojections in the MVA liquid crystal display device can be reduced, andthe leakage light in the dark state can be prevented.

Ninth Embodiment

Next, a liquid crystal display device according to a ninth embodimentwill be explained with reference to FIGS. 39A and 39B hereunder. In theseventh embodiment, as shown in FIG. 35, both the projections 217, 218are formed of dielectric material. In the ninth embodiment, a surface ofone projection is formed of conductive material and other configurationsare similar to the case in the seventh embodiment. In this case, thecompensating members 221, 222 shown in FIG. 35 may be arranged asoccasion demands.

FIG. 39A is a schematic partial sectional view showing a liquid crystaldisplay device according to the ninth embodiment. Projections 217 areformed on the pixel electrode 212 on the TFT substrate 235. A verticalalignment film 228 on the TFT substrate 235 side is formed to cover theprojections 217 and the pixel electrode 212. Projections 218 a formed ofdielectric material are formed on a surface of a color filter 251 on theopposing substrate 236 side.

A common electrode 254A is formed to cover the pixel electrode 212 andthe projections 218 a. The dielectric projection 218 a and a portion 218b of the common electrode 254A for covering the dielectric projections218 a constitute a CF substrate side projection 218. An alignment film228 on the opposing substrate 236 side is formed to cover the commonelectrode 254A.

FIG. 39B is a plan view showing the liquid crystal layer to show thetilt directions of the liquid crystal molecules when the voltage isapplied. When a predetermined voltage is applied between the pixelelectrode 212 and the common electrode 254A, the liquid crystalmolecules in the liquid crystal layer 229 are tilted. The liquid crystalmolecules 229 a in the neighborhood of the inclined surfaces of theprojections 217 are tilted such that end portions that are remote fromthe pixel electrode 212 are positioned far from the center of theprojection 217.

The surfaces of the projections 218 are formed of the conductivematerial, the electric field concentrates into the surfaces of theprojections 218 and thus equipotential surfaces are generated along thesurfaces of the projections 218. Therefore, the liquid crystal moleculesin the neighborhood of the surfaces of the projections 218 are falleninto the direction parallel to the surfaces of the projections 218. Theliquid crystal molecules 229 b in the neighborhood of the top surfacesof the projections 218 are affected equally by the liquid crystalmolecules on both sides of the projections 218. Therefore, the liquidcrystal molecules 229 b are tilted along the extending direction of theprojections 218.

The liquid crystal molecules in the area between the projections 217 andthe projections 218 are tilted in the middle direction between the tiltdirections of the liquid crystal molecules 229 a and the liquid crystalmolecules 229 b. That is, the liquid crystal molecules are aligned likea bend orientation in the direction of the substrate surface.

Like the liquid crystal display device shown in FIG. 8 in the prior art,the polarizing plates are cross-nicol-arranged on the outside of the TFTsubstrate 235 and the opposing substrate 236. The polarization axes 230of the polarizing plates intersect with the extending direction of theprojections 217 and the projections 218 in FIG. 39B by 45 degrees. Whenthe light transmits through the area, in which the liquid crystalmolecules are tilted in the direction in parallel with the polarizationaxes 230 of the polarizing plates, along the thickness direction of theliquid crystal layer, such light does not rotate the polarization axis.Therefore, the area in which the liquid crystal molecules are tilted tointersect with the polarization axis by 45 degrees becomes dark, andthus the black line appears between the projection 217 and theprojection 218.

The response time of the liquid crystal display device in the ninthembodiment measured when the display is changed from the dark state tothe ¼ half tone state and then returned again to the dark state isshorter than the response time of the MVA liquid crystal display deviceshown in FIG. 8 in the prior art. The reason for this may be consideredsuch that, since the liquid crystal molecules are bend-oriented in thesubstrate surface when the voltage is applied, the tilt direction can bedefined more quickly.

In the ninth embodiment, the tilt direction of the liquid crystalmolecules 229 b shown in FIG. 39B become parallel with the lengthdirection of the dielectric projections 218, but the vertical direction,i.e., the upward or downward direction in FIG. 39B is not decided.Therefore, there is the case where two domains in which the tiltdirection is different by 180 degrees are generated. If the locations ofdomain boundaries are not fixed, display quality is degraded. In orderto prevent the degradation of the display quality due to variation ofthe locations of the domain boundaries, another dielectric projectionsintersecting with the projections 217, 218 may be provided on theopposing surface of another substrate. Since the liquid crystalmolecules on both sides of the intersecting dielectric projections tendsto tilt toward two directions different by 180 degrees mutually, thedomain boundaries are fixed at positions of the projections thatintersect with the projections 217, 218.

In the above ninth embodiment, one projections are formed as theconductive projections. In place of the conductive projections, adielectric film that has smaller dielectric constant than that of theliquid crystal layer may be formed on the opposing surface and thenrecess patterns may be formed on a surface of the dielectric film. Inthis case, when the voltage is applied between the substrates, theelectric field having a distribution similar to the case where thedielectric projections are formed is generated. Therefore, the liquidcrystal molecule alignment similar to the case where the dielectricprojections are provided can be obtained.

Also, in the ninth embodiment, in order to define the boundaries of thedomains, the projections made of dielectric material are formed on theopposing surface of the substrate. But the slits may be formed in thepixel electrode in lieu of the formation of the projections. Thedistribution of the electric field in the neighborhood of the slits whenthe slits are formed in the pixel electrode is similar to thedistribution of the electric field generated in the case where thedielectric projections are provided. Therefore, even if the slits areformed in the pixel electrode, the alignment of the liquid crystalmolecules similar to the case where the dielectric projections areformed can be achieved.

As described above, according to the present invention, when the voltageis applied, the response characteristic can be improved by providing theprojections or the slits such that the liquid crystal molecules arebend-oriented in the direction of the substrate surface.

Tenth Embodiment

Next, a liquid crystal display device according to a tenth embodimentwill be explained with reference to FIG. 40 hereunder. FIG. 40 is aschematic partial sectional view showing the liquid crystal displaydevice according to the tenth embodiment. The configuration of the TFTsubstrate 235 is similar to that of the TFT substrate 235 shown in FIGS.39A and 39B in the ninth embodiment.

The common electrode 254 is formed on the surface of the color filter251 on the opposing substrate 236. The vertical alignment film 228B isformed to cover the surface of the common electrode 254B. The alignmentdefining force is destroyed or weakened in the area 228 a of thevertical alignment film 228B, that correspond to the conductiveprojections 218 in FIG. 39A. The area in which the alignment definingforce is destroyed or weakened is called a nonalignment defining area.The nonalignment defining area can be formed by irradiating selectivelythe energy beam such as ultraviolet laser, infrared laser, etc. onto thevertical alignment film, for example.

When the voltage is not applied, the liquid crystal molecules in thearea of the alignment film 228 b other than the nonalignment definingarea 228 a are aligned substantially perpendicularly to the substratesurface. Since the liquid crystal molecules that come into contact withthe nonalignment defining area 228 a have the weak vertical alignmentforce, they are tilted to the substrate surface. It seems that, sincethe liquid crystal molecules in the almost middle of the nonalignmentdefining area 228 a are affected by the liquid crystal molecules on bothsides, the tilt direction of the liquid crystal molecules becomeparallel with the length direction of the nonalignment defining area 228a.

When the voltage is applied between the substrates, the liquid crystalmolecules in the nonalignment defining area 228 a are largely tiltedtoward the length direction of the nonalignment defining area 228 a. Asa result, the nonalignment defining area 228 a can achieve the similareffect to the conductive projections 218 shown in FIG. 39A.

Eleventh Embodiment

Next, a liquid crystal display device according to an eleventhembodiment will be explained with reference to FIGS. 41A and 41Bhereunder.

FIG. 41A is a partial sectional view showing the liquid crystal displaydevice according to the eleventh embodiment. In the ninth embodiment, asshown in FIGS. 39A and 39B, the TFT substrate side projections 217 andthe CF substrate side conductive projections 218 are arrangedalternately in the substrate surface. In the eleventh embodiment, ifviewed along the normal direction of the substrate, the TFT substrateside projections 217 and the CF substrate side conductive projections218 are overlapped mutually.

FIG. 41B is a plan view showing the liquid crystal layer to show thetilt directions of liquid crystal molecules when the voltage is applied.If the predetermined voltage is applied between the pixel electrode 212and the common electrode 254A, the liquid crystal molecules in theliquid crystal layer 229 are tilted. The liquid crystal molecules 229 cin the neighborhood of the inclined surfaces of the projections 217 aretilted such that end portions that are remote from the pixel electrode212 are positioned far from the center of the projection 217. The liquidcrystal molecules 229 d in the neighborhood of the top portions of theprojections 218 are tilted toward the extending direction of theprojections 218. The liquid crystal molecules in the area between themiddle portions and the edge portions of the projections 217, 218 aretilted in the intermediate direction between the tilt direction of theliquid crystal molecules 229 c and the tilt direction of the liquidcrystal molecules 229 d. That is, the liquid crystal molecules aresplay-oriented in the neighborhood of the projections 217, 218.

In this manner, since the conductive projections 218 are arranged tooverlap with the conductive 217, the tilt direction of the liquidcrystal molecules in the almost middle area on the top portion of theprojections are restricted in the extending direction of the projections217, 218. Therefore, when the voltage is applied, the alignment changeof the liquid crystal molecules can be accelerated much more rather thanthe case where the conductive projections 218 are not provided.

In addition, since the TFT substrate side projections 217 and the CFsubstrate side conductive projections 218 are overlapped mutually, therelatively large electric field is generated between two projections.For this reason, it may be considered that the, alignment change of theliquid crystal molecules is carried out quickly and thus the responsecharacteristic can be improved.

Twelfth Embodiment

Next, a liquid crystal display device according to a twelfth embodimentwill be explained with reference to FIG. 42 and FIG. 43 hereunder.

FIG. 42 is a sectional view showing the liquid crystal display deviceaccording to the twelfth embodiment. The nonalignment defining area 228a is formed in a part of the alignment film 228 c on the TFT substrateside, and the dielectric projections 218 are formed on the surface ofthe common electrode 254 on the opposing substrate 236. If viewed alongthe normal direction of the substrate, the nonalignment defining area228 a and the dielectric projections 218 are overlapped mutually.

FIG. 43 is a plan view showing the liquid crystal display deviceaccording to the twelfth embodiment. The configurations of the gate busline 205, the drain bus line 207, the TFT 210, and the pixel electrode212 are similar to those in the liquid crystal display device shown inFIG. 33 according to the seventh embodiment. In FIG. 43, the descriptionof the capacitive bus line 208 shown in FIG. 33 is omitted. A sectionalview taken along a X—X dot-dash line in FIG. 43 corresponds to FIG. 42.The CF substrate side dielectric projections 218 and the nonalignmentdefining area 228 a extend longitudinally in the almost middle area ofthe pixel electrode 212 in the direction parallel to the drain bus line207.

If the voltage is applied between the pixel electrode 212 and the commonelectrode 254, liquid crystal molecules 229 e in the neighborhood of theinclined surfaces of the dielectric projections 218 are tilted such thatend portions that are remote from the opposing substrate 236 arepositioned far from the center of the dielectric projection 218. Theliquid crystal molecules 229 f in the neighborhood of the center portionof the nonalignment defining area 228 a are tilted in the lengthdirection (longitudinal direction in FIG. 43) of the nonalignmentdefining area 228 a. Hence, like the case of the eleventh embodimentshown in FIG. 41, the liquid crystal molecules are splay-oriented.Therefore, when the voltage is applied, the alignment change of theliquid crystal molecules can be accelerated much more rather than thecase where the nonalignment defining area 228 a is not provided.

The liquid crystal molecules 229 g in the neighborhood of the edgeportions of the pixel electrode 212 are tilted toward the inside of thepixel electrode 212 by the disturbance of the electric field so as toorthogonally intersect with the edges. The liquid crystal moleculesbetween the longitudinal edges of the pixel electrode 212 and thedielectric projections 218 are tilted in the middle direction betweenthe tilt direction of the liquid crystal molecules 229 f and the tiltdirection of the liquid crystal molecules 229 g.

In FIG. 43, the liquid crystal molecules in the neighborhood of theupper and lower edge portions of the pixel electrode 212 are tiltedtoward the inside of the pixel electrode 212. Therefore, the tiltdirection of the liquid crystal molecules 229 f in the middle portion ofthe projections 218 is defined in the longitudinal direction in FIG. 43,but their directions are opposite mutually. As a result, domainboundaries are generated in the inside of the pixel. Since thedielectric projections are arranged between the alignment film 228C ofthe TFT substrate 235 in FIG. 42 and the pixel electrode 212 so as toorthogonally intersect with the nonalignment defining area 228 a, thedomain boundaries can be fixed at the positions of the dielectricprojections.

Thirteenth Embodiment

Next, a liquid crystal display device according to a thirteenthembodiment will be explained with reference to FIG. 44 hereunder.

FIG. 44 is a plan view showing the liquid crystal display deviceaccording to the thirteenth embodiment. The configurations of the gatebus line 205, the drain bus line 207, the TFT 210, and the pixelelectrode 212 are similar to those in the liquid crystal display deviceshown in FIG. 33 according to the seventh embodiment. In FIG. 44, thedescription of the capacitive bus line 208 shown in FIG. 33 is omitted.The nonalignment defining area 228 b is formed in a part of thealignment film on the TFT substrate and the opposing substrate. In thiscase, the projections for defining the domain boundaries are not formedon both substrates.

The shape of the pixel electrode 212 has notches to match with the shapeof the TFT 210, but is basically approximated by a rectangle. Thenonalignment defining areas 228 b extend from respective corners of therectangle toward the inside of the pixel. The nonalignment definingareas 228 b extending from respective corners are coupled mutually inthe inside of the pixel.

The tilt directions of the liquid crystal molecules in the neighborhoodof two sides intersecting with one corner of the pixel electrode 212 arenot parallel mutually. Therefore, the domain boundaries are generatedbetween two sides. In the thirteenth embodiment, since the nonalignmentdefining areas 228 b extend from the corners toward the inside of thepixel, such nonalignment defining areas 228 b act as the domainboundaries. That is, one domain can be defined by one side of the pixelelectrode 212 and the nonalignment defining areas 228 b.

In the thirteenth embodiment, the locations of the domain boundaries arerestricted by the nonalignment defining areas 228 b without theprojections. Accordingly, reduction in the optical transmittance due tothe projections can be prevented.

Fourteenth Embodiment

Next, a liquid crystal display device according to a fourteenthembodiment will be explained with reference to FIGS. 45A and 45Bhereunder.

FIGS. 45A and 45B are plan views showing a local portion in one pixel ofthe liquid crystal display device according to the fourteenthembodiment. Two nonalignment defining areas 228 c in which the alignmentdefining force of the vertical alignment film is destroyed or weakenedare arranged in parallel with each other. When the voltage is notapplied, as shown in FIG. 45A, the liquid crystal molecules 229 ipositioned between two nonalignment defining areas 228 c are alignedsubstantially perpendicularly to the substrate surface.

The liquid crystal molecules 229 h on the inside of the nonalignmentdefining area 228 c are tilted slightly from the perpendicular directionsince the vertical alignment defining force in this area is weak. Thetilt direction coincides with the length direction of the nonalignmentdefining area 228 c. This may be considered such that, since the tiltdirection is affected equally by the liquid crystal molecules on bothsides of the nonalignment defining areas 228 c, such tilt direction isnot shifted to one of both sides. Accordingly, it seems that, if theinfluence by the liquid crystal molecules on both sides is weakened, thetilt direction of the liquid crystal molecules on the inside of thenonalignment defining areas 228 c become random. In order to restrictthe tilt direction of the liquid crystal molecules by the nonalignmentdefining areas 228 c, the width must be reduced narrower than a certainupper limit value. According to the experiment made by the inventors ofthis application, when the width of the nonalignment defining area 228 cis 5 μm, the liquid crystal molecules on the inside are tilted to thelength direction of the nonalignment defining areas 228 c.

FIG. 45B shows the alignment states of the liquid crystal molecules whenthe voltage is applied. The liquid crystal molecules on the inside ofthe nonalignment defining areas 228 c are largely tilted to the inclineddirection when the voltage is not applied. The liquid crystal molecules229 i between two nonalignment defining areas 228 c are affected by theinclination of the liquid crystal molecules 229 h and are tilted to thedirection parallel to the length direction of the nonalignment definingareas 228 c.

In this way, it is possible to restrict the tilt direction of the liquidcrystal molecules by providing not the nonalignment defining areas 228 cbut the projections. Since the projections are not provided, reductionin the optical transmittance due to the projections can be prevented.

With the use of JALS-684 manufactured by JSR Inc. as the alignment filmand MJ961213R manufactured by Merck Inc. as the liquid crystal material,the liquid crystal cell in which a width of the nonalignment definingarea 228 c is 5 μm, an interval is 35 μm, and a cell thickness is 4.25μm is fabricated. The polarizing plates are cross-nicol-arranged suchthat their polarizations axis directions intersect with the lengthdirection of the nonalignment defining area 228 c by an angle of 45degrees. After the transmittance of the liquid crystal display device ismeasured, the maximum transmittance in excess of 25% has been confirmed.Here, the intensity of the ultraviolet rays irradiated to form thenonalignment defining area 228 c is 4000 mJ/cm².

Fifteenth Embodiment

Next, a liquid crystal display device according to a fifteenthembodiment will be explained with reference to FIG. 46 hereunder.

FIG. 46 is a plan view showing the alignment state of the liquid crystalmolecules in the light state of the liquid crystal display deviceaccording to the fifteenth embodiment. The liquid crystal display deviceaccording to the fifteenth embodiment is different from the liquidcrystal display device according to the fourteenth embodiment in that achiral agent is added into the liquid crystal layer. Otherconfigurations are similar to those in the liquid crystal display deviceaccording to the fourteenth embodiment. CM31 manufactured by Chisso Inc.is employed as the chiral agent, and a concentration of the chiral agentused in the liquid crystal material is set to 4.8 wt %.

It has been found that, when the light state of the liquid crystaldisplay device according to the fifteenth embodiment is monitored, thelight transmits through the center portion of the nonalignment definingarea 228 c and thus four dark lines appear between two neighboringnonalignment defining areas 228 c. Since the areas in which the tiltdirections of the liquid crystal molecules are parallel with thepolarization axes of the polarizing plates do not exhibit the doublerefraction property, such areas are the dark areas even when the voltageis applied. The reason for the appearance of four dark lines is that thedirector directions of the liquid crystal molecules are twisted incompliance with the displacement from one nonalignment defining area 228c to the neighboring nonalignment defining area 228 c. Also, it seemsthat the liquid crystal molecules are tilted to the length direction ofthe nonalignment defining area 228 c in the center portion of thenonalignment defining area 228 c. A twisted angle may be 360 degreesbetween the neighboring nonalignment defining areas 228 c because thenumber of the dark lines is four.

In the fifteenth embodiment, since the dark line appears in the lightstate, no improvement can be found in a respect of the transmittancerather than the prior art. However, it is expected that, since the tiltdirection of the liquid crystal molecules is decided by the chiralagent, the response speed from the dark state to the half tone state canbe accelerated.

Sixteenth Embodiment

FIG. 47 is a plan view showing an MVA liquid crystal display deviceaccording to a sixteenth embodiment of the present invention. FIG. 48 isa sectional view showing the liquid crystal display device. In thiscase, FIG. 48 shows a sectional shape at a position taken along a XI—XIline in FIG. 47. FIG. 47 shows one pixel of the liquid crystal displaydevice, and a chain double-dashed line in FIG. 47 denotes a position ofthe projection (a domain defining projection and an auxiliaryprojection) formed on the opposing substrate side.

A plurality of gate bus lines 312 are formed in parallel with each otheron a glass substrate (TFT substrate) 311. Also, capacitive bus lines 313are formed in parallel with gate bus lines 312 between the gate buslines 312 respectively. In addition, a gate electrode 316 g of the TFT316 is formed on the glass substrate 311. The gate electrode 316 g isconnected to the gate bus line 312. The gate bus line 312, the gateelectrode 316 g, and the capacitive bus line 313 are formed on the samewiring layer (first wiring layer). That is, the gate bus line 312, thegate electrode 316 g, and the capacitive bus line 313 are formed bypatterning the same conductive film. Also, the gate bus line 312, thegate electrode 316 g, and the capacitive bus line 313 are covered with afirst insulating film (gate insulating film) 314 formed on the glasssubstrate 311.

A silicon film (not shown) serving as the active area of the TFT 316 isformed on the first insulating film 314 over the gate electrode 316 g.Also, a plurality of drain bus lines 315, and a source region 316 s anda drain region 316 d of the TFT 316 are formed on the insulating film314. The drain bus lines 315 are formed to orthogonally intersect withthe gate bus lines 312. The source region 316 s and the drain region 316d are formed on both sides of the silicon film over the gate electrode316 g to be separated mutually. Then, the drain region 316 d isconnected to the drain bus line 315.

Rectangular areas partitioned by the gate bus lines 312 and the drainbus lines 315 are pixel areas respectively. The drain bus lines 315, andthe source region 316 s and the drain region 316 d are formed on thesame wiring layer (second wiring layer). The drain bus lines 315 and theTFT 316 are covered with the second insulating film 317 formed on thefirst insulating film 314.

The pixel electrodes 318 are formed on the second insulating film 317every pixel area. For example, the pixel electrodes 318 are formed oftransparent conductor such as ITO, etc. Slits 319 aligned on a straightline extending in the oblique direction are formed in the pixelelectrode 318. In the sixteenth embodiment, the slits 319 are arrangedin a vertically symmetric fashion in one pixel electrode 318. Also, thepixel electrode 318 is connected electrically to the source electrode316 s via a contact hole formed in the second insulating film 317.

A vertical alignment film 320 is formed on the pixel electrode 318. Thevertical alignment film 320 is formed polyimide, for example. Asdescribed later, a process for revealing partially (a shaded portion 321in FIG. 47) a pre-tilt angle (pre-tilt angle revealing process) isapplied to the alignment film 320. As the pre-tilt angle revealingprocess, for example, there are UV irradiation, rubbing process, or thelike. By applying the pre-tilt angle revealing process, under thecondition that the voltage is not applied, the liquid crystal moleculesare tilted to the predetermined direction and an angle between thealignment film 320 and the director of the liquid crystal molecules(pre-tilt angle) is more than 45 degrees and less than 90 degrees. Inthe sixteenth embodiment, the preferable range of the pre-tilt angle is87 to 89 degrees.

In contrast, a black matrix 332 is formed under the glass substrate(opposing substrate) 331. The areas of the gate bus lines 312, thecapacitive bus lines 313, the drain bus lines 315, and the TFTs 316 onthe TFT substrate side and the outside area of the display area arelight-shielded by the black matrix 332. In the sixteenth embodiment, itis assumed that the black matrix 332 is formed of a light-shieldingmetal film such as Cr (chromium), etc. However, the black matrix 332 maybe formed of black resin. In addition, the black matrix 332 may beformed by laminating at least two-colored color filters out of red (R),green (G), and blue (B) color filters, to be described later.

Any one one-colored color filter 333 of red (R), green (G), and blue (B)color filters is formed under the glass substrate 331 every pixel. Inthe sixteenth embodiment, it is assumed that the red (R), green (G), andblue (B) color filters are arranged repeatedly in sequence in thehorizontal direction and also the same-colored color filters arearranged in the vertical direction.

The common electrode 334 common to respective pixel electrodes is formedunder the color filter 333. The common electrode 334 is also formed oftransparent conductor such as ITO, etc. The domain defining projections(also called banks) 336 are formed under the common electrode 334. Asshown in FIG. 47, the projections 336 are arranged at the middleposition between the slits 319 provided in the pixel electrode 318 onthe TFT substrate side. Also, auxiliary projections (called auxiliarybanks) 336 a are formed at positions that coincide with both edgeportions of the pixel electrode 318 in the horizontal direction, moreparticularly, portions at which the projections 336 form an obtuse anglewith the edge of the pixel electrode 318. The auxiliary projections 336a are formed simultaneously of the same material as the domain definingprojections 336.

The vertical alignment film 335 is formed under the glass substrate 331.Surfaces of the common electrode 334, the projections 336, and theauxiliary projections 336 a are covered with the alignment film 335. Thealignment film 335 is formed of polyimide, for example.

Liquid crystal material 329 having the negative dielectric anisotropy issealed between the TFT substrate (glass substrate 311) and the opposingsubstrate (glass substrate 331). Spherical spacers having a uniformdiameter, for example, are arranged between the TFT substrate (glasssubstrate 311) and the opposing substrate (glass substrate 331), so thata distance (cell gap) between the TFT substrate and the opposingsubstrate is kept constant. Also, the polarizing plate (not shown) isarranged below the TFT substrate (glass substrate 311) and over theopposing substrate (glass substrate 331) respectively.

In the sixteenth embodiment, the pre-tilt angle revealing process isapplied to the portion of the alignment film 320 on the TFT substrateside, which are the edge portions of the pixel electrode 318 on bothsides in the horizontal direction and at which the projections 336 havean obtuse angle with the edge of the pixel electrode 318 (in otherwords, portions at which the slit series have an acute angle with theauxiliary projections 336 a), and the adjacent pixel side half area onthe inside of the slit 319 a whose end portion on the pixel side next tothe right side in FIG. 47 (referred to as the “adjacent pixel”hereinafter) is closed and which is closest to the adjacent pixel(shaded area indicated by a reference 321 in FIG. 47). The effectobtained by applying the pre-tilt angle revealing process to these areaswill be explained with reference to schematic views of the pixelelectrode shown in FIG. 49 to FIG. 51. In this case, in FIG. 49 to FIG.51, it is indicated that the black dot portions of the liquid crystalmolecules 328 are directed to the common electrode side.

If there is no positional displacement when the TFT substrate and theopposing substrate are stuck together, the auxiliary projections 336 aon the adjacent pixel side are arranged to coincide with the edge of thepixel electrode 318, as shown in FIG. 49. The liquid crystal molecules328 are aligned in the direction perpendicular to the inclined surfaceof the auxiliary projections 336 a in the neighborhood of the auxiliaryprojections 336 a. Also, the liquid crystal molecules in the half areaof the slit 319 a whose end on the adjacent pixel side is closed andwhich is closest to the adjacent pixel on the adjacent pixel side areaffected by the liquid crystal molecules 328 in the neighborhood of theauxiliary projections 336 a and then aligned in the predetermineddirections (directions shown in FIG. 49 respectively).

In the case that the auxiliary projections 336 a are not provided orpositions of the auxiliary projections 336 a are displaced toward theadjacent pixel side as shown in FIG. 50, when the voltage is appliedbetween the pixel electrode 318 and the common electrode 334, the liquidcrystal molecules in the neighborhood of the edge of the pixel electrode318 are tilted to the direction (direction indicated by an arrow B inFIG. 50) to which the liquid crystal molecules 328 on the inside of theslit 319 b closest to the drain bus line 315 of the adjacent pixel aretilted. However, since this direction is different from the direction towhich the liquid crystal molecules are tilted by the electric fieldgenerated by the drain bus line 315 of the adjacent pixel, the alignmentbecomes unstable and thus the response characteristic is degraded or thealignment failure is generated.

As shown in FIG. 51, if the pre-tilt angle revealing process is appliedthe alignment film 320 in the portion 321 in which the alignment of theliquid crystal molecules becomes unstable due to the lateral electricfield generated by the drain bus line 315 of the adjacent pixel, i.e.,the inner portion of the slit 319 a on the adjacent pixel side and theportion in which the projections 336 form an obtuse angle with the edgeof the pixel electrode 318, the liquid crystal molecules are hardlyaffected by the lateral electric field generated by the drain bus line315 of the adjacent pixel since the liquid crystal molecules are tiltedto the predetermined direction (direction indicated by an arrow C inFIG. 51) in the initial state. As a result, the alignment failure can beavoided and the response characteristic can be improved.

Next, a method of manufacturing the liquid crystal display deviceaccording to the sixteenth embodiment will be explained with referenceto FIG. 47 and FIG. 48 hereunder.

First, the gate bus line 312, the gate electrode 316 g and thecapacitive bus line 313 are formed by forming a Cr film of about 150 nmthickness, for example, as a conductive film on the glass substrate (TFTsubstrate) 311 by the PVD (Physical Vapor Deposition) method and thenpatterning the conductive film by the photolithography.

Then, an insulating film 314 serving as the gate insulating film of theTFT 316, an n⁻-type amorphous silicon film serving as the active regionof the TFT 316, and an insulating film serving as the channel protectionfilm are formed in sequence on the overall upper surface of the glasssubstrate 311 by the plasma CVD method.

The insulating film 314 is formed of silicon nitride (SiN) or siliconoxide (SiO₂), for example, to have a thickness of about 100 to 600 nm.Also, a thickness of the n⁻-type amorphous silicon film is about 15 to50 nm. In addition, the insulating film serving as the channelprotection film is formed of silicon nitride, for example, to have athickness of about 50 to 200 nm.

Then, the channel protection film is formed by patterning the uppermostlayer of the insulating film by the photolithography. Then, theconductive film having a triple-layered structure of Ti, Al and Ti isformed by forming an n⁺-type amorphous silicon film serving as an ohmiccontact layer of the TFT 316 to have a thickness of about 30 nm, andthen stacking Ti, Al, and Ti in sequence on the n⁺-type amorphoussilicon film by the PVD method. For example, a thickness of theunderlying Ti layer is 20 nm, a thickness of the Al layer is 75 nm, anda thickness of the overlying Ti layer is 20 nm. This conductive film maybe formed of Al, Al alloy, or other low resistance metal.

Then, a resist film having a predetermined pattern is formed on theconductive film by using the photoresist. Then, as shown in FIG. 48, thesource electrode 316 s and the drain electrode 316 d of the TFT 316 aswell as the drain bus lines 315 are formed by etch the conductive film,the n⁺-type amorphous silicon film, and the n⁻-type amorphous siliconfilm using the resist film as an etching mask. The conductive film, then⁺-type amorphous silicon film, and the n⁻-type amorphous silicon filmare etched by the dry etching using a mixed gas of Cl₂ and BCl₃, forexample. After this, the resist film used as the etching mask isremoved.

Then, for example, a silicon nitride film as the insulating film(protection film) 317 is formed on the overall upper surface of theglass substrate 311 by the CVD method to have a thickness of about 100to 600 nm. Then, a contact hole is formed in the insulating film 317 toreach the source electrode 316 s of the TFT 316.

Then, the ITO film of about 70 nm thickness is formed on the overallupper surface of the glass substrate 311 by the PVD method. Then, asshown in FIG. 47, the pixel electrode 318 having the slits 319 is formedby patterning the ITO film by the photolithography.

In turn, the alignment film 320 is formed on the overall upper surfaceof the glass substrate 311. Then, the pre-tilt angle revealing processis applied to predetermined portions (portions indicated by a reference321 in FIG. 47) of the alignment film 320. As the pre-tilt anglerevealing process, there are the UV irradiation and the rubbing process,for example. If the pre-tilt angle is revealed by the UV irradiation,material in which the pre-tilt angle is revealed by the UV irradiation,e.g., polyimide or polyamic acid that is alignment film material for theUV alignment is used as alignment film material, then covering theportions of the alignment film 320 other than the predetermined portions321 with the light-shielding mask, and then irradiating the polarized UVonto the substrate 311 from the oblique direction, e.g., the directionindicated by an arrow C in FIG. 51. According to the material of thealignment film 320, the pre-tilt angle can be revealed by irradiatingthe non-polarized UV.

In contrast, if the pre-tilt angle is revealed by the rubbing process,for example, an alignment film JALS684 manufactured by JSR Inc. is usedas alignment film material, then areas of the alignment film 320 otherthan the predetermined portions 321 is covered with the resist mask,etc., and then surfaces of the predetermined portions 321 of thealignment film 320 are rubbed by the nylon brush, etc. along thepredetermined direction, e.g., the direction indicated by an arrow C inFIG. 51. At this time, the pre-tilt angle can be changed by adjustingthe revolution number of the brush, the rubbing depth and the number ofrubbing. In this manner, the TFT substrate can be completed.

In contrast, the opposing substrate having the projections 336, 336 a isprepared. The opposing substrate can be manufactured by the well knownmethod. More particularly, the black matrix 332 having a predeterminedpattern is formed of light shielding material such as Cr, etc. on theglass substrate 331. Then, the red (R), green (G), and blue (B) colorfilters 333 are formed on the glass substrate 331 and then the commonelectrode 334 is formed of ITO on the color filters 333. Then, thedomain defining projections 336 and the auxiliary projections 336 a areformed on the common electrode 334, and then the surfaces of the commonelectrode 334, the projections 336, and the auxiliary projections 336 aare covered with the alignment film 334 formed of polyimide.Accordingly, the opposing substrate can be completed.

Subsequently, the opposing substrate on which the domain definingprojections are provided and the TFT substrate formed in the abovemanner are stuck together, and then the liquid crystal material issealed between both substrates. Accordingly, the liquid crystal displaydevice according to the sixteenth embodiment can be completed.

In the above manufacturing method, the projections 336 and the auxiliaryprojections 336 a are formed of photoresist. But they are not limited tothe above. For example, the projections 336 and the auxiliaryprojections 336 a may be formed of dielectric material except for thephotoresist.

As described above, according to the liquid crystal display device ofthe present invention, the domain defining projections are provided onone substrate and the slits are formed on the electrode of the othersubstrate, and also the pre-tilt angle revealing process is applied tothe alignment film on the other substrate in the area in which thealignment of the liquid crystal molecules becomes unstable by thelateral electric field from the bus line. Therefore, the alignmentfailure due to the lateral electric field from the bus line can beavoided, and the large aperture ratio, the good viewing anglecharacteristic, and the good picture quality can be achieved.

Seventeenth Embodiment

FIG. 52 is a plan view showing a liquid crystal display device accordingto a seventeenth embodiment of the present invention. A difference ofthe seventeenth embodiment from the sixteenth embodiment is that theslits formed in the pixel electrode have a different shape, and thus theexplanation of portions overlapped with the sixteenth embodiment will beomitted. Also, in FIG. 52, the case is shown where the auxiliaryprojections 336 a are arranged at the positions deviated to the drainbus line 315 side of the adjacent pixel.

In the seventeenth embodiment, as shown in FIG. 52, the shape of theslit 319 b which is formed in the pixel electrode 318 and is closest tothe adjacent pixel (i.e., the slit whose end portion on the adjacentpixel side is opened) has a taper shape in which a width of the endportion on the adjacent pixel side (referred to as the rear end sidehereinafter) is wide and a width of the end portion opposite to theadjacent pixel (referred to as the, top end side hereinafter) is narrow.Also, the slit 319 that is adjacent to the slit 319 b, i.e., the slit319 a whose rear end side is closed and which is closest to the adjacentpixel, has a shape having a large width on the rear end side. That is,in the seventeenth embodiment, a width of the top end side of the slit319 b is set wider than that of the rear end side of the slit 319 a.

When the voltage is applied between the pixel electrode 318 and thecommon electrode 334, as shown in FIG. 52, the liquid crystal molecules328 on the inside of the slit 319 b are tilted toward the directionindicated by an arrow D in FIG. 52. In contrast, the liquid crystalmolecules 328 on the rear end side of the slit 319 b are tilted towardthe direction indicated by an arrow E in FIG. 52. At this time, sincethe width of the slit 319 b on the rear end side is larger than that ofthe slit 319 b on the top end side and also the number of the liquidcrystal molecules 328 on the rear end side of the slit 319 b is largerthan that of the liquid crystal molecules 328 on the top end side of theslit 319 b, the liquid crystal molecules 328 on the rear end side of theslit 319 b are aligned in the predetermined direction (directionindicated by an arrow E). Also, the liquid crystal molecules in theneighborhood of the slit 319 b are also affected by the liquid crystalmolecules 328 on the inside of the slit 319 b and then aligned in thepredetermined direction. Therefore, the alignment failure can beavoided.

In the seventeenth embodiment, as described above, it is featured thatthe slit 319 b and the slit 319 b that are close to the adjacent pixelare formed like a taper shape. If the pre-tilt angle revealing processis applied to the predetermined portion of the alignment film, like thesixteenth embodiment, in addition to that the slit 319 b and the slit319 b are formed like a taper shape, the alignment failure due to thelateral electric field from the drain bus line 315 of the adjacent pixelcan be prevented without fail.

Besides, in the sixteenth and seventeenth embodiments, the slits areformed in the pixel electrode on the TFT substrate side and the domaindefining projections and the auxiliary projections are provided on theopposing substrate side. But the present invention is not limited to theabove. For example, the present invention may be applied to the liquidcrystal display device in which the domain defining projections and theauxiliary projections are provided on the pixel electrode on the TFTsubstrate side and the slits are formed in the common pixel electrode onthe opposing substrate side.

According to the liquid crystal display device of the present invention,the domain defining projections are provided on one substrate and alsothe slits are formed in the electrode on the other substrate, and thewidth of the end portion of the first slit closest to the bus line ofthe adjacent pixel on the opposite side to the bus line is set smallerthan the width of the end portion of the second slit adjacent to thefirst slit on the bus line side. Therefore, the alignment failure due tothe lateral electric field from the bus line of the adjacent pixel canbe avoided, and the large aperture ratio, the good viewing anglecharacteristic, and the good picture quality can be achieved.

Eighteenth Embodiment

An eighteenth embodiment of the present invention will be explainedhereunder.

In Patent Application Publication (KOKAI) Hei 11-84414, it has beenproposed that the distribution of the dielectric constant of the resinis arranged symmetrically by changing gradually. However, there is nodisclosure about the optimum combination with the projections and theslits.

FIG. 53 is a plan view showing a liquid crystal display device accordingto an eighteenth embodiment of the present invention, and FIG. 54 is aschematic sectional view showing the liquid crystal display deviceaccording to the eighteenth embodiment. In this case, in FIG. 53 andFIG. 54, the same references are affixed to the same constituentelements as the sixteenth embodiment. Also, in FIG. 54, illustration ofthe insulating film and the alignment film on the TFT substrate side andthe black matrix, the color filter, the alignment film, etc. on theopposing substrate side is omitted.

Like the sixteenth embodiment, the gate bus line 312, the drain bus line315, the TFT 316, the pixel electrode 318 and the vertical alignmentfilm are formed on the TFT substrate 311 side. Also, the domain definingslits 319 are formed in the pixel electrode 318. As shown in FIG. 53,these domain defining slits 319 are arranged such that they are alignedon a straight line extending in the oblique direction and are positionedsymmetrically in one pixel electrode 318.

In contrast, the black matrix, the color filter, and the commonelectrode 334 are formed on the opposing substrate side, and thedielectric film 338 of about 2 to 3 μm thickness is formed under thecommon electrode 334. The dielectric film 338 consists of a lowdielectric constant portion 338 a and a high dielectric constant portion338 b. The low dielectric constant portion 338 a is arranged in parallelwith the slit 319 in the middle between the domain defining slits 319 onthe TFT substrate 311 side. Also, the high dielectric constant portion338 b is arranged in the remaining area (containing the portion opposingto the slit 319). Then, the relative dielectric constant of the lowdielectric constant portion 338 a is 3.0, for example, and the relativedielectric constant of the high dielectric constant portion 338 b is3.5, for example.

As a method of forming the dielectric film 338 having the portions whoserelative dielectric constant is different mutually, following methodsmay be considered.

As a first method, there is a method of patterning the substances havingdifferent relative dielectric constant by the lithography. Moreparticularly, the high dielectric constant portion 338 b is formed byforming the SiN film by the CVD method and then patterning the SiN filmby the photolithography. Then, the photoresist is coated as material ofthe low dielectric constant portion 338 a, and then the resist filmcoated on the high dielectric constant portion 338 b is removed via theexposing and developing steps. Accordingly, the dielectric film 338having the low dielectric constant portion 338 a and the high dielectricconstant portion 338 b is formed. In this case, the relative dielectricconstant of the SiN is about 7 and the relative dielectric constant ofthe resist is about 3.

As a second method, there is a method of changing partially the relativedielectric constant of the dielectric film by irradiating the light ontothe dielectric film. For example, the dielectric film 338 is formed bycoating polyvinyl cinnamate or polyimide having the photoreaction group,etc. on the common electrode 334. In the case of polyvinyl cinnamate,the bridge reaction is accelerated by irradiating the light and thus therelative dielectric constant of the light-irradiated portion isenhanced. In contrast, in the case of material that is split by thelight such as polyimide, a molecular weight of the light-irradiatedportion is reduced and thus the dielectric constant is lowered. As thematerial whose dielectric constant is changed by the light irradiation,there are acrylic resin (methacrylate), and others.

FIG. 55 is a view showing equipotential lines when the voltage isapplied between the pixel electrode and the common electrode. As shownin FIG. 55, the equipotential lines are pushed out to the outside fromthe liquid crystal layer in the portion of the slit 319 of the pixelelectrode 318 and the low dielectric constant portion 338 a in thedielectric film 338 (portion encircled by a broken line in FIG. 55).Because the liquid crystal molecules having the negative dielectricanisotropy tend to be aligned along the equipotential lines, as shown inFIG. 54, the alignment direction of the liquid crystal molecules isdifferent respectively on both sides of the slit 319 and the lowdielectric constant portion 338 a, whereby alignment division (multidomain) can be attained.

In the eighteenth embodiment, since the alignment division (multidomain) can be attained by the dielectric film 338 having the lowdielectric constant portion 338 a and the high dielectric constantportion 338 b in place of the domain defining projections, the apertureratio can be improved and the liquid crystal display device which isbright and has high resolution can be implemented. Also, the portionshaving the different dielectric constant can be relatively easily formedby the photolithography or the light irradiation.

FIG. 56 is a graph showing the result to check whether or notdisclination is generated after the dielectric film 338 is formed byusing two type dielectric materials. In FIG. 56, dielectric materialthat is arranged at the positions opposing to the slits is used as thefirst dielectric material, and dielectric material that is arranged inthe middle of the slits is used as the second dielectric material.

As shown in FIG. 56, the relative dielectric constant of the seconddielectric material is lower than that of the first dielectric material.If difference of relative dielectric constant between them is less than0.5, no disclination is generated, but the area which has the unstablealignment state is generated.

In addition, if the relative dielectric constant of the seconddielectric material is lower than that of the first dielectric materialby more than 0.5, the disclination is not generated and the good displayquality can be derived. If the relative dielectric constant of thesecond dielectric material is equal Lo or higher than that of the firstdielectric material, the disclination is generated.

In case the high dielectric constant portion 338 b is arranged in themiddle of the slits 319 and also the low dielectric constant portion 338a is arranged in the area opposing to the slit 319, as shown in FIG. 57,the disclination is generated as the singular point of the alignmentstate in the indefinite positions from the edge of the high dielectricconstant portion 338 b to the slit 319 (e.g., position encircled by abroken line in FIG. 57). Thus, there are caused the problems such thatthe display luminance is dark, the response is slow, etc. Accordingly,the low dielectric constant portion 338 a must be arranged in the middleof the slits 319, the high dielectric constant portion 338 b must bearranged in the position opposing to the slit 319, and the difference inthe relative dielectric constant between the low dielectric constantportion 338 a and the high dielectric constant portion 338 b must be setto more than 0.5.

FIGS. 58A and 58B and FIG. 59 show a variation of the eighteenthembodiment respectively. FIG. 58A shows an example in which the lowdielectric constant portion 338 a is arranged in parallel with the gatebus line 312 in the middle of the pixel. FIG. 58B shows an example inwhich the low dielectric constant portion 338 a is arranged in parallelwith the drain bus line 315 in the middle of the pixel. In both cases,the dielectric film is formed on the opposing substrate side and thedifference in the relative dielectric constant between the portion withthe high dielectric constant and the portion with the low dielectricconstant is set to more than 0.5. Accordingly, like the eighteenthembodiment, the disclination can be prevented.

FIG. 59 shows an example in which portions 338 c with the middledielectric constant (relative dielectric constant is 3.25) are arrangedbetween the low dielectric constant portion 338 a (relative dielectricconstant is 3) arranged in the middle of the slits 319 and the highdielectric constant portion 338 b (relative dielectric constant is 3.5)arranged to oppose to the slits. In this case, the similar effect to theabove can be achieved.

In the above embodiments, the case is explained where the slits areformed in the pixel electrode on the TFT substrate side and thedielectric film having the portions with the different relativedielectric constant is formed on the opposing substrate side. However,if the dielectric film is formed on the TFT substrate side and thedomain defining slits or projections are provided on the commonelectrode on the opposing substrate side, the same effect as the aboveembodiments can be obtained. Also, the dielectric film having theportions with the different relative dielectric constant may be formedon both the TFT substrate and the opposing substrate. In this case, theportion of the dielectric film with the low dielectric constant on theopposing substrate side is arranged so as to oppose to the portion ofthe dielectric film with the high dielectric constant on the TFTsubstrate side, and also the portion of the dielectric film with thehigh dielectric constant on the opposing substrate side is arranged soas to oppose to the portion of the dielectric film with the lowdielectric constant on the TFT substrate side.

According to the liquid crystal display device of the present invention,since the domain defining portions are formed on one substrate and thedielectric film having the portion with the high dielectric constant andthe portion with the low dielectric constant is formed on the othersubstrate, the alignment division (multi domains) can be attained by thedomain defining portions and the dielectric film. Therefore, the largeaperture ratio can be achieved and the good viewing angle characteristicand the good picture quality can be obtained.

1. A thin film transistor substrate comprising: a storage capacitanceforming electrode formed on a first substrate; an active element formedon the first substrate; and a pixel electrode formed on the firstsubstrate to be connected to the active element, and divided into atleast three areas by slits; wherein electrical connection of one area ofthe three areas of the pixel electrode to another area has a pluralityof routes passing through different areas and at least two of the routesof the electrical connection are provided to oppose electrically to thestorage capacitance forming electrode.
 2. A thin film transistorsubstrate according to claim 1, wherein areas of the pixel electrodesopposing to the storage capacitance forming electrode are different. 3.A thin film transistor substrate according to claim 1, whereinthicknesses of dielectric layers are different in areas opposing to thestorage capacitance forming electrode every route opposing to thestorage capacitance forming electrode.
 4. A thin film transistorsubstrate according to claim 1, wherein storage capacitance values aredifferent every route opposing to the storage capacitance formingelectrode.
 5. A liquid crystal display device including a thin filmtransistor substrate set forth in any one of claims 1 to 4.